Patent Publication Number: US-11032223-B2

Title: Filtering electronic messages

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/597,404, filed May 17, 2017. This application also relates to the following co-pending applications: U.S. patent application Ser. No. 13/185,943 (U.S. Pat. No. 8,844,010), filed Jul. 19, 2011; U.S. patent application Ser. No. 13/349,287, filed Jan. 12, 2012; U.S. patent application Ser. No. 14/457,421 (U.S. Pat. No. 9,641,474), filed Aug. 12, 2014; U.S. patent application Ser. No. 14/684,954, filed Apr. 13, 2015 (U.S. Pat. No. 9,508,054); U.S. patent application Ser. No. 14/684,658, filed Apr. 13, 2015 (U.S. Pat. No. 9,563,915); U.S. patent application Ser. No. 14/519,919, filed Oct. 21, 2014 (U.S. Pat. No. 9,563,904); U.S. patent application Ser. No. 14/519,975, filed Oct. 21, 2014; International Patent Application No. PCT/US15/56013, filed Oct. 16, 2015; U.S. patent application Ser. No. 15/277,933, filed Sep. 27, 2016; U.S. patent application Ser. No. 15/420,096, filed Jan. 31, 2017; and U.S. patent application Ser. No. 15/422,999, filed Feb. 2, 2017. 
    
    
     BACKGROUND 
     People purchase products from many different merchants using a variety of different payment options. The transactions for these purchases typically are confirmed by physical in-store receipts or by electronic confirmation messages that are addressed to the purchasers&#39; messaging accounts (e.g., a purchaser&#39;s electronic mail account). The large number and diversity of confirmation messages makes it difficult for people to track their purchases and obtain a comprehensive understanding of their purchase histories. In addition, the large diversity of merchants from which people purchase products makes it difficult for merchants to obtain sufficient purchase history data to develop accurate customer profiles. Even assuming that a person uses a common identifier (e.g., a loyalty card or credit card) for all his or her purchases, these purchases typically are tracked only by the merchant that issued the identifier to the customer. This lack of customer information limits the ability to effectively determine customers&#39; cross-merchant purchase transaction information. 
     In an effort to ameliorate these problems, reporting systems have been developed to extract purchase related information from data sources that are published directly by merchants to consumers, such as purchase confirmation messages and shipping confirmation messages. 
     SUMMARY 
     The invention features a method, performed by computer apparatus, for processing a population of electronic messages transmitted between network nodes and stored in association with respective user accounts on one or more network data storage systems managed by one or more messaging servers, each electronic message being associated with a respective sender, a respective header, and a respective body. In accordance with this method, headers in the population that are stored on one or more of the network data storage systems are fetched by a client network node from one or more of the messaging servers, across multiple of the user accounts. For each of one or more senders, the fetched headers that are associated with the sender are grouped into clusters based on a density based clustering process that correlates the clusters with respective dense regions in a clustering data space in which the fetched headers are separated from one another based on similarities between respective pairs of the fetched headers. For each of one or more of the clusters, a respective sample of the electronic messages in the population that are associated with the fetched headers in the cluster and stored on one or more of the network data storage systems are retrieved by a client network node from one or more of the messaging servers. Each electronic message in the retrieved sample is classified by a machine learning classifier with a respective label from a predefined set of labels comprising one or more purchase related labels and an associated confidence level to create a respective classification data set for the cluster. The cluster is assigned a respective cluster label selected from the predefined set of labels based on at least one cluster classification rule that maps the respective classification data set to the respective cluster label. For each of one or more clusters assigned a respective one of the purchase related labels, a respective filter for filtering purchase related electronic messages is automatically generated. 
     The invention also features a method, performed by computer apparatus, for processing a population of electronic messages transmitted between network nodes and stored in association with respective user accounts on one or more network data storage systems managed by one or more messaging servers, each electronic message being associated with a respective sender, a respective header, and a respective body. In accordance with this method, for each of one or more senders, headers in the population are fetched from one or more of the network data storage systems. For each of one or more senders, the fetched headers are grouped into clusters. The process of grouping the fetched headers comprises assigning ones of the fetched headers to respective ones of the clusters based on similarities between the headers in the clusters without regard to any message body content. For each of one or more of the clusters, a respective sample of one or more of the electronic messages associated with the fetched headers assigned to the cluster is retrieved from one or more of the network data storage systems, and the cluster is designated by a machine learning classifier as either receipt-related or not-receipt-related based on header and body content of the one or more retrieved electronic messages in the sample. A respective electronic message filter is automatically generated for each of one or more of the clusters designated as receipt-related, wherein each electronic message filter defines a respective rule for matching a respective pattern of subject field strings in a header of an electronic message. 
     In some examples one or more of the filters are installed by a processor in at least one network communication channel to select purchase related electronic messages from a set of electronic messages stored in association with respective user accounts on one or more network data storage systems managed by one or more messaging servers. 
     The invention also features computer apparatus operable to implement the methods described above and computer-readable media storing computer-readable instructions causing computer apparatus to implement the methods described above. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagrammatic view of an example of a network communication environment. 
         FIG. 2  is a diagrammatic overview of electronic message processing stages performed by an example of a purchase transaction data retrieval system. 
         FIG. 3  is a diagrammatic view of an example of an electronic message. 
         FIG. 4  is a flow diagram of an example of a process for generating an electronic message filter. 
         FIG. 5  is a diagrammatic view of data relating to different stages of the electronic message filter generation process of  FIG. 4 . 
         FIG. 6  is a flow diagram of an example of a process for generating an electronic message filter. 
         FIG. 7  is a diagrammatic view of an example of a system for generating an electronic message filter. 
         FIG. 8  is a diagrammatic view of an example of clusters of headers in a clustering data space. 
         FIG. 9  is a flow diagram of an example of a process for grouping electronic message headers into clusters. 
         FIG. 10  is a diagrammatic view of an example of a system for generating an electronic message filter. 
         FIG. 11  is a flow diagram of an example of a process for generating an electronic message filter. 
         FIG. 12  is a block diagram of an example of computer apparatus. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, like reference numbers are used to identify like elements. Furthermore, the drawings are intended to illustrate major features of exemplary embodiments in a diagrammatic manner. The drawings are not intended to depict every feature of actual embodiments nor relative dimensions of the depicted elements, and are not drawn to scale. 
     I. Definition of Terms 
     A “product” is any tangible or intangible good or service that is available for purchase or use. 
     An “electronic message” is a persistent text based information record sent from a sender to a recipient between physical network nodes and stored in non-transitory computer-readable memory. An electronic message may be structured (e.g., a hypertext markup language (HTML) message that includes structured tag elements) or unstructured (e.g., a plain text message). 
     A “purchase related electronic message” is an electronic message that relates to purchasing a product. Examples of purchase related electronic messages include order confirmations, shipping confirmations, refunds, cancellations, backorders, coupons, and promotions. 
     A “sender domain” in an electronic message refers to the administrative realm for a messaging address from which the electronic message is sent. For example, an electronic message address may have a format “local-part@domain”, where the “local-part” identifies the messaging address and the “domain” identifies the administrative realm for the messaging address. Multiple messaging addresses may share the same sender domain. 
     A “receipt” is an electronic message that confirms the status of a purchase of one or more products. Examples of receipts include order confirmation electronic messages and shipping confirmation electronic messages. 
     “Purchase transaction information” (also referred to as “purchase transaction data”) is information related to the purchase of a product. Purchase transaction data includes, for example, invoice data, purchase confirmation data, product order information (e.g., merchant name, order number, order date, product description, product name, product quantity, product price, sales tax, shipping cost, and order total), and product shipping information (e.g., billing address, shipping company, shipping address, estimated shipping date, estimated delivery date, and tracking number). 
     A “computer” is any machine, device, or apparatus that processes data according to computer-readable instructions that are stored on a computer-readable medium either temporarily or permanently. “Computer apparatus” refers to one or more distinct computers. A “computer operating system” is a software component of a computer that manages and coordinates the performance of tasks and the sharing of computing and hardware resources. A “software application” (also referred to as software, an application, computer software, a computer application, a program, and a computer program) is a set of instructions that a computer can interpret and execute to perform one or more specific tasks. A “data file” is a block of information that durably stores data for use by a software application. 
     The term “computer-readable medium” (also referred to as “memory”) refers to any tangible, non-transitory device capable storing information (e.g., instructions and data) that is readable by a machine (e.g., a computer). Storage devices suitable for tangibly embodying such information include, but are not limited to, all forms of physical, non-transitory computer-readable memory, including, for example, semiconductor memory devices, such as random access memory (RAM), EPROM, EEPROM, and Flash memory devices, magnetic disks such as internal hard disks and removable hard disks, magneto-optical disks, DVD-ROM/RAM, and CD-ROM/RAM. 
     A “network node” is a physical junction or connection point in a communications network. Examples of network nodes include, but are not limited to, a terminal, a computer, and a network switch. A “server system” includes one or more network nodes and responds to requests for information or service. A “client node” is a network node that requests information or service from a server system. 
     As used herein, the term “includes” means includes but not limited to, the term “including” means including but not limited to. The term “based on” means based at least in part on. 
     II. Filtering Purchase Related Electronic Messages 
     A. Introduction 
     People send and receive nearly 200 billion emails per day worldwide. Only a small fraction of these emails, however, relate to purchases. As a result, substantial amounts of time and resources are needed to sift through users&#39; message accounts to identify and retrieve purchase related emails in quantities that are sufficient to obtain current actionable information on a regular basis. 
     The examples that are described herein provide improved systems and methods for discovering and filtering purchase related electronic messages transmitted between physical network nodes to convey purchase related information to designated recipients. These systems and methods solve practical problems that have arisen as a result of the proliferation of different electronic message formats used by individual merchants and across different merchants. In this regard, these examples are able to automatically learn the structures and semantics of machine generated electronic message headers, which accelerates the ability to support new message sources, new markets, and different languages. These examples provide a purchase related electronic message discovery and filtering service that is able to identify and filter purchase related electronic messages with high accuracy across a wide variety of electronic message formats. 
     Examples that are described herein leverage insights regarding the distinctive structural features of machine-generated purchase related electronic messages to implement a process for automatically discovering and filtering purchase related electronic messages that improves the operation of computer apparatus to achieve dramatic reductions in processing resources, data storage resources, network resources, and filter production times compared to conventional approaches. In some examples, improvements result from configuring a computer apparatus to perform a unique sequence of specific electronic message processing rules in a network communications environment. In some examples, additional benefits over conventional approaches are realized by configuring the computer apparatus to automatically learn the individual peculiarities of different machine-generated purchase related electronic messages sent by different merchants and automatically adapt the processing to those peculiarities. Some examples, for instance, substantially increase the accuracy and efficiency of the message discovery process by automatically adjusting the operation of the computer apparatus to accommodate different levels of diversity in the respective templates used by different merchants to generate their respective sets of machine-generated purchase related electronic messages. 
     In specific examples, these systems and methods include improved special purpose computer apparatus programmed to automatically learn, from a set of electronic messages, an electronic message filter that matches to the headers of purchase related electronic messages that are generated by a machine according to a respective message template that defines the structural elements in the bodies of the purchase related electronic messages. These systems and methods also include improved special purpose computer apparatus programmed to install the learned electronic message filters in at least one network communication channel to select purchase related electronic messages from a set of electronic messages stored in association with respective user accounts on one or more network data storage systems managed by one or more messaging servers. 
     By these improved systems and methods, product purchase information can be identified and extracted from a wide variety of electronic message types and aggregated to provide individuals with enhanced tools for visualizing and organizing their purchase histories and to provide merchants and other organizations improved cross-merchant purchase information across different consumer demographics to enable targeted and less intrusive advertising and other marketing strategies. These improved systems and methods can be deployed to monitor consumer purchases over time to obtain updated purchase history information that can be aggregated for an individual consumer or across many consumers to provide actionable information that directs consumer behavior and organizational marketing strategies. For example, these improved systems and methods can organize disparate product purchase information extracted from individual electronic messages into actionable data that can be used by a consumer to organize her prior purchases and enhance her understanding of her purchasing behavior and can be used by merchants and other organizations to improve the accuracy and return-on-investment of their marketing campaigns. 
     B. Exemplary Operating Environment 
       FIG. 1  shows an example of a network communications environment  10  that includes a network  11  that interconnects a purchase transaction data retrieval system  12 , one or more product merchants  14  that sell products, one or more product delivery providers  16  that deliver purchased products to purchasers, one or more message providers  18  that provide message handling services, and one or more purchase transaction information consumers  20  that purchase product and market information and services from the purchase transaction data retrieval system  12 . 
     The network  11  may include any of a local area network (LAN), a metropolitan area network (MAN), and a wide area network (WAN) (e.g., the internet). The network  11  typically includes a number of different computing platforms and transport facilities that support the transmission of a wide variety of different media types (e.g., text, voice, audio, and video) between network nodes of the purchase transaction data retrieval system  12 , the one or more product merchants  14 , the product delivery providers  16 , the message providers  18 , and the purchase transaction information consumers  20 . Each of the purchase transaction data retrieval system  12 , the product merchants  14 , the product delivery providers  16 , the message providers  18 , and the purchase transaction information consumers  20  typically connects to the network  11  via a network node (e.g., a client computer or server system) that includes a tangible computer-readable memory, a processor, and input/output (I/O) hardware (which may include a display). 
     One or more of the product merchants  14  typically allow individuals and businesses to purchase products directly over the network  11  using a network enabled software application, such as a web browser. One or more of the product merchants  14  also may allow individuals and businesses to purchase products in a physical retail establishment. In either case, after a purchase transaction has been completed, a product merchant  14  may send a product purchase confirmation electronic message to a messaging address associated with the product purchaser. The product purchase confirmation message may include, for example, product order information such as merchant name, order number, order date, estimated delivery date, product description, product name, product quantity, product price, sales tax, shipping cost, and order total. The product merchants  14  also may arrange to have the product delivered by one of the product delivery providers  16 . Depending on the type of product that was purchased, the product delivery provider  16  may deliver the product to the purchaser physically or electronically. In either case, the product delivery provider  16  or the product merchant  14  may send a delivery notification electronic message to the messaging address associated with the purchaser. The delivery notification electronic message may include, for example, product shipping information such as product order information, billing address, shipping company, shipping address, estimated shipping date, estimated delivery date, and tracking number. 
     In general, the purchaser&#39;s messaging address may be any type of network address to which electronic messages may be sent. Examples of such messaging addresses include electronic mail (e-mail) addresses, text messaging addresses (e.g., a sender identifier, such as a telephone number or a user identifier for a texting service), a user identifier for a social networking service, and a facsimile telephone number. The purchase related electronic messages typically are routed to the purchaser through respective ones of the message providers  18  associated with the purchaser&#39;s messaging address. The message providers  18  typically store the purchaser&#39;s electronic messages in a respective message folder in association with the purchaser&#39;s messaging address on one or more network data storage systems managed by one or more messaging servers. 
     The purchase transaction data retrieval system  12  extracts purchase transaction information from the electronic messages of product purchasers. In some examples, the purchase transaction data retrieval system obtains authorization from the product purchasers to access their respective message folders that are managed by the message providers  18 . In other examples, product purchasers allow the purchase transaction data retrieval system  12  to access their electronic messages that are stored on their local communication devices (e.g., personal computer or mobile phone). 
     Referring to  FIG. 2 , after obtaining authorization to access the electronic messages  22  of a purchaser, the purchase transaction data retrieval system  12  processes the electronic messages  22  through a number of stages before producing processed data  24  that is provided to the purchase transaction information consumers  20 . These stages include a message discovery stage  26 , a field extraction stage  28 , and a data processing stage  30 . 
     In the message discovery stage  26 , the purchase transaction data retrieval system  12  identifies the electronic messages  22  that relate to product purchases. In some examples, rule-based filters and machine learning classifiers are used to identify purchase related electronic messages. 
     In the field extraction stage  28 , the purchase transaction data retrieval system  12  extracts product purchase information from the identified ones of the electronic messages  22 . Examples of such product purchase information include merchant name, order number, order date, product description, product name, product quantity, product price, sales tax, shipping cost, order total, billing address, shipping company, shipping address, estimated shipping date, estimated delivery date, and tracking number. 
     In the data processing stage  30 , the purchase transaction data retrieval system  12  processes the extracted product purchase information according to the different types of purchase transaction information consumers  20 . For example, for individual users, the extracted product purchase information is processed, for example, to display information about the users&#39; purchases, including information for tracking in-transit orders, information for accessing purchase details, and aggregate purchase summary information. For advertisers, the extracted product purchase information is processed, for example, to assist in targeting advertising to consumers based on their purchase histories. For market analysts, the extracted product purchase information is processed to provide, for example, anonymous item-level purchase detail across retailers, categories, and devices. 
     C. Discovering and Filtering Purchase Related Electronic Messages 
     In the examples explained in detail below, the purchase transaction information data retrieval system  12  includes a filter learning system that automatically learns electronic message filters that match the headers of respective sets of similar purchase related electronic messages, such as sets of electronic messages that are generated by a machine according to respective message templates that respectively define the structural elements of the purchase related electronic messages. 
       FIG. 3  shows an example of a confirmation electronic message  32  for a product order. The confirmation electronic message  32  includes a header  34  and a body  35 . The header  34  includes the following standard structural elements: “From:”; “To:”; “Date:”; and “Subject”. The header also includes one or more of the following structural elements, which are not shown in  FIG. 3 : “Cc:”, “Content-Type”, “Precedence:”, “Message-ID:”, “In-Reply-To:”, “References:”, “Reply-To:”, “Archived-At:”, “Received:”, and “Return-Path:”. The body  36  includes the following merchant-specific machine-generated structural elements: an introductory “Dear”  36 ; standard informational text  37  (i.e., “Thank you for placing your order . . . once your item has been shipped.”); “Order Number:”  38 ; “Order Summary”  40 ; “Product Subtotal:”  42 ; “Discounts:”; “Shipping Charges:”  46 ; “Tax:”  48 ; “Total:”  50 ; “Part No”  52 ; “Product Price”  54 ; “Discount”  56 ; “Part No”  58 ; “Product Price”  60 ; and “Discount”  62 . The structural elements  34 - 50  are static elements and the sets of structural elements  52 - 56  and  58 - 62  include the same static elements that repeat in respective iterating elements. The non-structural elements (e.g., prices, order number, and part numbers) of the electronic message are data fields that are extracted and classified by a parser component of the product purchase information provider  12 . 
       FIG. 4  shows an example of a method  66  of automatically building one or more electronic message filters. In accordance with this method, computer apparatus processes a population of electronic messages transmitted between network nodes and stored in association with respective user accounts on one or more network data storage systems managed by one or more messaging servers. Each of the electronic messages in the population is associated with a respective sender, a respective header, and a respective body. 
     In the illustrated example, the computer apparatus is programmed to perform the method of  FIG. 4  for each of one or more electronic message senders ( FIG. 4 , block  68 ). A sender may correspond to a single electronic message address (e.g., sales@store.com) or a sender domain (e.g., *@store.com), which may be associated with multiple electronic messages addresses. 
     The computer apparatus fetches headers from one or more of the network data storage systems ( FIG. 4 , block  70 ). The fetched headers may be associated with a particular sender domain or may be fetched without regard to the sender domain. The computer apparatus groups the fetched headers into clusters (FIG.  4 , block  72 ). In this process, for each sender, ones of the fetched headers are assigned to respective ones of the clusters based on similarities between the headers in the clusters without regard to any message body content. For each of one or more of the clusters ( FIG. 4 , blocks  74 ,  80 ), the computer apparatus retrieves, from one or more of the network data storage systems, a respective sample of one or more of the electronic messages associated with the fetched headers assigned to the cluster ( FIG. 4 , block  76 ). The computer apparatus also designates, with a machine learning classifier, the cluster as either receipt-related or not-receipt-related based on header and body content of the one or more retrieved electronic messages in the sample ( FIG. 4 , block  78 ). The computer apparatus automatically generates a respective electronic message filter for each of one or more of the clusters designated as receipt-related, where each electronic message filter defines a respective rule for matching a respective pattern of subject field strings in a header of an electronic message while crawling electronic messages stored in association with respective user accounts on one or more data storage systems managed by one or more network data storage systems ( FIG. 4 , block  82 ). 
     The approach illustrated in  FIG. 4  involves three main stages: (i) a header structure learning stage that groups headers into clusters of electronic messages having similar structural elements; (ii) a sample-based classification stage that accurately identifies which of the clusters of headers correspond to one or more purchase related electronic message types; and (iii) a filter generation stage. Processing complete electronic messages (including, e.g., headers and bodies) consumes substantially more resources than processing the headers alone. Through sampling, the number of complete electronic messages that are retrieved and then processed in the classification stage can be significantly reduced. In this way, the method of  FIG. 4  is able to achieve dramatic reductions in the processing resources, data storage resources, network resources, and filter production times required to build electronic message filters compared to conventional approaches. In addition, since the system only retrieves headers and a small sample of the complete electronic messages that correspond to header clusters (which typically correspond to machine-generated electronic messages, such as receipts), the system is unlikely to inadvertently retrieve users&#39; personal electronic messages and thereby inherently protects user privacy. 
     This approach leverages the inherent structural nature of machine-generated electronic messages to produce high-accuracy filters even though the headers are classified based only on a sample of the complete electronic messages that are associated with each cluster. In particular, when applied to machine-generated electronic messages, the header structure learning stage can generate tight clusters of electronic message headers that are likely to have been produced by the same message template. As a result, only a few or even only one sample complete electronic message is needed to represent each cluster in the classification stage. 
       FIG. 5  shows an exemplary diagrammatic view of the data processed at different stages of the filter building method of  FIG. 4 . In this example, the fetching stage  84  involves fetching all 10 million of the headers in an example population of electronic messages that correspond to a particular sender domain. The clustering stage  86  involves clustering the 10 million headers into 200 header clusters. The cluster classification stage  88  involves retrieving 2000 complete electronic messages that correspond to a respective predetermined fixed size sample of 10 electronic messages for each of the 200 clusters, and classifying the respective electronic message sample with a machine learning classifier. The filter generation stage  90  involves building a respective filter for each cluster that is classified as being related to a purchase. Thus, in this hypothetical example, the number (i.e., 2000) of complete electronic messages that are processed to generate the electronic message filters amounts to only 0.02% of the total number of electronic messages in the population, which results in a dramatic reduction in processing resources, data storage resources, network resources, and filter production times compared to conventional approaches. 
     In some examples, these substantial benefits result, at least on part, from programming the computer apparatus with specific computer-readable instructions that improve the way in which the computer apparatus identifies purchase-related electronic messages headers. In some cases, the purchase-related header identification capabilities of the computer apparatus are by provisioning the computer apparatus with specific instructions that cause the computer apparatus to group electronic message headers into tight clusters and, subsequently, use a machine learning classifier to identify purchase-related header clusters based on a small sample of the complete electronic messages that are associated with each header cluster. 
       FIG. 6  shows a flow diagram of an example 98 of the electronic message filter building process of  FIG. 4 . In accordance with this method, computer apparatus processes a population of electronic messages transmitted between network nodes and stored in association with respective user accounts on one or more network data storage systems managed by one or more messaging servers. Each of the electronic messages in the population is associated with a respective sender, a respective header, and a respective body. 
     In this example, computer apparatus are programmed to perform one or more elements of the method of  FIG. 6  based on electronic messages from one or more electronic message senders ( FIG. 6 , block  100 ). As mentioned above, a sender may correspond to a single electronic message address (e.g., sales@store.com) or to a sender domain (e.g., *@store.com), which may be associated with multiple electronic messages addresses. 
     In accordance with the method of  FIG. 6 , computer apparatus (e.g., a client network node) fetches, from one or more of the messaging servers, headers in the population that are associated with the sender and stored on one or more of the network data storage systems across multiple of the user accounts ( FIG. 6 , block  102 ). In some examples, the computer apparatus fetches all of the electronic message headers in the population of electronic messages. In other examples, the computer apparatus fetches one or more samples of the electronic message headers in the population. 
     Before fetching the headers, the computer apparatus typically obtains authorization to access the users&#39; messaging accounts, either directly from the users or indirectly from a third party service, such as an access authorization service. The computer apparatus then uses the access authorization to fetch headers that are associated with the sender from the users&#39; messaging accounts. In some examples, the computer apparatus implements an electronic message crawling engine that crawls the users&#39; messaging accounts (e.g., by calling an electronic messaging API), and parses and evaluates contents of the electronic message headers. In some examples, the electronic message crawling engine parses one or both of the “From:” field and the “Subject:” field and applies one or more filters (e.g., regular expression filters) to the parsed results to identify the headers that correspond to the target sender. 
     The computer apparatus groups the fetched headers into clusters based on a density based clustering process that correlates the clusters with respective dense regions in a clustering data space in which the fetched headers are separated from one another based on similarities between respective pairs of the fetched headers ( FIG. 6 , block  104 ). In general, any density based clustering process may be used. In some examples, the iterative clustering process described below in connection with  FIGS. 8 and 9  is used to cluster the fetched headers. In other examples, the computer apparatus clusters the fetched headers using the Density-Based Spatial Clustering of Applications with Noise (DBSCAN) clustering process. 
     In some examples, the computer apparatus pre-processes the subject fields in the electronic message headers before grouping the headers into clusters. In some examples, the computer apparatus tokenizes the text-based contents of the subject fields in the headers by extracting contiguous strings of symbols (e.g., symbols representing alphanumeric characters) separated by white spaces. The contiguous symbol strings typically correspond to words and numbers. In some examples, the computer apparatus normalizes the contents of the subject fields by replacing capital letters with lower case letters, removing punctuation, and replacing tokens that match patterns for integers and real numbers in the electronic message headers with wildcard tokens. In some examples, integers are replaced with the wildcard token “INT” and real numbers are replaced with the wildcard token “FLOAT”. The normalization of the subject fields improves the ability of the computer apparatus to discover purchase related electronic messages. 
     In some examples, the similarities between respective pairs of the fetched headers are determined based on measures of content similarity that compare similarity and diversity of the contents of pairs of strings in the headers of the electronic messages. In some of these examples, the subject field of each header is decomposed into a set of bigrams (i.e., two-word phrases). In some of these examples, the similarity measure corresponds to the Jaccard similarity coefficient, which measures similarity between two headers based on the size of the intersection divided by the size of the union of bigrams in the headers. 
     After the headers have been grouped into clusters, the computer apparatus performs the following processes for each of one or more of the clusters ( FIG. 6 , block  108 ). 
     The computer apparatus (e.g., a client network node) retrieves, from one or more of the messaging servers, a respective sample of the electronic messages in the population that are associated with the fetched headers in the cluster and stored on one or more of the network data storage systems ( FIG. 6 , block  108 ). In some examples, the computer apparatus retrieves a predetermined fixed number (e.g., 10, 5, or 1) of electronic messages for each cluster. In other examples, the computer apparatus retrieves a variable number of electronic messages for each cluster that depends on, for example, a statistical measure that characterizes the headers in the cluster. 
     The computer apparatus classifies, with a machine learning classifier, each electronic message in the retrieved sample with a respective label from a predefined set of labels comprising one or more purchase related labels and an associated confidence level to create a respective classification data set for the cluster ( FIG. 6 , block  110 ). 
     In some examples, the machine learning classifier is trained on a bag-of-words representation of purchase-related electronic messages using a supervised machine learning model (e.g., a logistic regression model or a naïve Bayes model). In some of these examples, the bag-of-words representation includes descriptive features that describe a particular purchase related electronic message. In some examples, each feature represents a string (e.g., a word) and the number of times the string appears in a predefined dictionary. In some examples, the dictionary includes: words or n-grams in the subject fields; aspects of the sender address (e.g., the text before the “@” sign); words in the message bodies; and number of images in the message bodies. 
     In some examples, the predefined set of labels consists of labels that indicate whether an electronic message is receipt-related or is not-receipt-related. An exemplary label set of this type is: {“receipt,” “unknown”}. In other examples, the machine learning classifier is configured to classify an electronic message into different categories of purchase-related electronic messages. An exemplary label set of this type includes some or all of the following labels {“order notification,” “shipping notification,” “refund,” “cancellation,” “back order,” “coupon,” “promotion,” “unknown”}. 
     In some examples, for each cluster, the machine learning classifier assigns to each of the sampled electronic messages a respective predicted label selected from the predefined set of labels and an associated confidence level for the predicted label. The respective classification data set for each cluster includes the set of predicted labels for the corresponding sample of electronic messages and their associated label confidence levels. 
     The computer apparatus assigns to each cluster a respective cluster label selected from the predefined set of labels based on at least one cluster classification rule that maps the respective classification data set to the respective cluster label ( FIG. 6 , block  112 ). In some examples, a cluster classification rule instructs the computer apparatus to label a cluster with a particular label based on one or more confidence factors, such as the number of the electronic messages in the corresponding sample that are assigned the same label, and the confidence levels associated with the assigned labels. According to an example of such a cluster classification rule, a cluster is labeled with a particular label if the particular label is assigned to all of the electronic messages in the sample with a respective confidence level that satisfies a threshold confidence level (e.g., 98% or higher). In some examples, if the confidence factors for a particular cluster do not satisfy the confidence thresholds, the electronic messages in the cluster are flagged for manual classification. 
     In some examples, in response to a determination that a predicted label for a particular electronic message is below a threshold confidence level, the computer apparatus flags the particular electronic message for manual classification. In some examples, the manually labeled electronic messages are used to extend the training set of the machine learning classifier. 
     For each cluster that is assigned a respective purchase related label, the computer apparatus automatically generates a respective filter for filtering purchase related electronic messages ( FIG. 6 , block  116 ). In some examples, the process of generating a filter involves identifying common substrings within the headers in the respective cluster, and generating a respective filter (e.g., a regular expression filter) based on the identified substrings. Each filter typically defines a matching pattern for a respective set of subject field strings in an electronic message. In some examples, sequence mining is used to create filters based on an analysis of n-grams (i.e., continuous sequences of n items for a given sequence of text) in headers. These examples involve determining respective counts of the n-grams that appear in the subject fields of the headers in each cluster, and incorporating into the respective filter one or more of the n-grams that are associated with prominent counts (e.g., the n-grams appear in a high percentage of the headers). In some of these examples, the sequence mining involves analyzing bigrams in the subject fields of the headers. An example of a method for automatically generating a respective filter from each cluster is described below in connection with  FIG. 11 . 
     After generating a respective filter for each purchase related cluster, a processor may install one or more of the filters in at least one network communication channel to select purchase related electronic messages from a set of electronic messages stored in association with respective user accounts on one or more network data storage systems managed by one or more messaging servers. In some examples, the computer apparatus implements an electronic message crawling engine that crawls the users&#39; messaging accounts, and parses and evaluates contents of the electronic message headers. In some examples, the electronic message crawling engine parses the “From:” and “Subject:” header fields of the users&#39; electronic messages and applies one or more of the generated filters (e.g., regular expression filters) to the parsed results to identify the purchase related headers that correspond to the target sender. The electronic message crawling engine then retrieves the complete electronic messages corresponding to the identified purchase related headers. In some examples, each filter is associated with a respective set of one or more electronic message body extraction parsers. In these examples, for each filter matched to a respective one of the electronic messages in the set, the computer apparatus attempts to parse the electronic message body with the one or more electronic message body extraction parsers that are associated with the matched filter. Exemplary message body extraction parsers are described in U.S. Pat. Nos. 8,844,010, 9,563,915, and 9,563,904. 
       FIG. 7  shows a diagrammatic view of an example of a system  118  for building a message filter. The system  118  is operable to process a population of electronic messages transmitted between network nodes and stored in association with respective user accounts (e.g., alice, bob, clark, dan, eric, peter, and rob) on one or more network data storage systems  122 ,  124 ,  126  that are managed by respective messaging servers (e.g., Message Provider  1 , Message Provider  2 , . . . , Message Provider M). 
     The system  118  includes a header sampler  120  that fetches, for each of one or more senders, a respective sample of headers in the electronic message population that are associated with the sender and stored on one or more of the network data storage systems  122 - 126  across multiple of the user accounts. By fetching only a sample of the available headers instead of fetching all of the headers that are associated with the sender, the header sampler  120  improves the operation of the computer apparatus by reducing the processing resources, data storage resources, network resources, and production times needed to build electronic message filters. In other examples, the header sampler  120  fetches a sample of headers across sender domains. 
     A pre-processor  128  pre-processes the subject fields in the fetched sample of electronic message headers before the headers are grouped into clusters. In some examples, the pre-processor  128  performs one or more of the pre-processing steps described above in connection with the fetching process described above in connection with the method of  FIG. 6 . In some examples, the pre-processor  122  also de-duplicates the header data by treating all headers that have identical subject field content as a single instance. In this way, the pre-processor  128  further reduces the processing resources, data storage resources, network resources, and production times needed to build electronic message filters. 
     A cluster engine  130  groups the pre-processed headers in the sample into clusters by sender domain. In some examples, the grouping is based on a density based clustering process that correlates the clusters with respective dense regions in a clustering data space in which the pre-processed headers are separated from one another based on similarities between respective pairs of the pre-processed headers. In some examples, the similarities between respective pairs of the fetched headers are determined based on measures of content similarity that compare similarity and diversity of the contents of in the headers of the electronic messages. Exemplary header contents that are compared include the text (e.g., strings, n-grams, and/or words) in the subject field and the sender messaging address. In some of these examples, the similarities between the subject fields of two headers are measured using the Jaccard similarity coefficient, which measures similarity between two headers based on the size of the intersection divided by the size of the union of bigrams in the subject fields. 
     Referring to  FIG. 8 , the computed similarity scores between each pair of pre-processed headers determine how close the headers are to one another in the clustering data space  132 . In some examples, the clustering process involves identifying connected components in a graph, where there is a link between circular nodes (representing headers) if their joint similarity score is greater than a threshold similarity level.  FIG. 8  shows an example of a sample of twenty pre-processed headers that are grouped into twelve clusters (shown enclosed by dashed lines). 
       FIG. 9  shows an alternative clustering process that uses a variable similarity threshold to iteratively determine an optimal set of links between headers that inherently accounts for the respective variabilities in the machine-generated electronic messages generated by different senders. 
     The clustering process begins by setting the current similarity threshold level to an initial similarity threshold value T 0  ( FIG. 9 , block  140 ). In some examples, the similarity threshold corresponds to the Jaccard similarity measure. In some examples, the initial similarity threshold value T 0  is set to an initial level on a similarity scale of 0 to 1. In some of these examples, the initial similarity threshold T 0  is in the range 0.6≤T 0 ≤0.8. 
     Next, the headers in the sample are grouped into clusters in a set C 0  based on the current threshold level T 0  ( FIG. 9 , block  142 ), and a count N 0  of the clusters in the set of grouped clusters in the set C 0  is stored ( FIG. 9 , block  144 ). In some examples, the process of grouping the headers includes calculating similarity scores between respective pairs of the fetched messages headers based on comparisons of text (e.g., strings, n-grams, and/or words) in the subject fields of the respective message headers, and grouping the fetched headers into clusters based on comparisons of the calculated similarity scores with the current threshold level. 
     A second iteration of the process is repeated with another threshold T 1  ( FIG. 9 , blocks  146 ,  148 ,  142 ,  144 ). In some examples, for each iteration, the current threshold is lower than the preceding threshold. The set of thresholds {T i } may be determined dynamically (e.g., based on a mathematical formula or algorithm) or may be predetermined. In some examples, each successive threshold value is determined by decrementing the preceding threshold by a predetermined fixed amount (e.g. 0.1 on a similarity scale of 0 to 1). 
     In the second iteration of the clustering process, the headers in the sample are re-grouped into a set of clusters C 1  based on the current threshold level T 1  ( FIG. 9 , block  142 ) and a count N 1  of the clusters in the set of grouped clusters C 2  is stored ( FIG. 9 , block  144 ). The clusters in C 1  that consist of headers with unique subject lines are identified, and a count M 1  of all the identified headers in C 1  that consist of headers with unique subject lines is determined ( FIG. 9 , block  150 ). In some examples, a header is determined to have a unique subject line if the subject line does not have any words in common with the subject lines of the other headers in the cluster. In other examples, unique subject field lines are identified based on other text-based comparisons of the subject field content, such as comparisons between the strings or n-grams in the subject field lines of the headers in the cluster. 
     If the number M j  of headers in the clusters that consist of headers that have unique subject lines is greater than a threshold M TH  ( FIG. 9 , block  152 ), the number of unique subject lines is deemed to be too large and the clusters in the preceding set of clusters (i.e., C i-1 ) are returned by the cluster engine  130  as the output cluster set  160  for the current sample of headers ( FIG. 9 , block  156 ). Also, if the count N i  of the clusters in the current iteration and the count N i-1  of the clusters in the preceding iteration satisfy a similarity criterion ( FIG. 9 , block  152 ), the number of clusters is deemed to have converged and the clusters in the preceding set of clusters (i.e., C i-1 ) are returned by the cluster engine  130  as the output cluster set  160  for the current sample of headers ( FIG. 9 , block  156 ). 
     In some examples, the similarity criterion compares the ratio of the difference between the current and preceding cluster counts to the number of clusters in the preceding iteration. In some of these examples, the similarity criterion corresponds to: 
     
       
         
           
             
               
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     If neither of the tests in blocks  152  and  154  is satisfied, another iteration of the clustering process is repeated with the next clustering threshold ( FIG. 9 , block  148 ). 
     Referring back to  FIG. 7 , after the cluster engine  130  has grouped the sample of headers into clusters  160 , an electronic message sampler  162  selects a respective sample of the headers in each header cluster  160  and retrieves the complete electronic messages  164  that are associated with the selected headers from the message providers. The result is a respective sample i of electronic messages  164  for each cluster i of headers  160 . 
     For each sample i of electronic messages  164 , an electronic message classifier  166  classifies each of the constituent electronic messages in the sample. In some examples, the electronic message classifier  166  is a machine learning classifier of the type described above in connection with  FIGS. 4 and 6 . The machine learning classifier assigns to the electronic messages in each sample  164  a respective set  168  of labels and associated confidence levels. In some examples, in response to a determination that a predicted label for a particular electronic message is below a threshold confidence level, the computer apparatus flags the particular electronic message for manual classification ( FIG. 7 , block  170 ). In some examples, the manually labeled electronic messages are used to train the electronic message classifier  166 . 
     In some examples, a cluster classification rule instructs the computer apparatus to label a cluster with a particular label based on one or more confidence factors, such as the number of the electronic messages in the corresponding sample that are assigned the same label and the confidence levels associated with the assigned labels. In some examples, if the confidence factors do not satisfy the one or more confidence thresholds ( FIG. 7 , block  172 ), the electronic messages in the cluster are flagged for manual classification ( FIG. 7 , block  170 ). 
     For each cluster that is assigned a respective purchase related label ( FIG. 7 , block  174 ), the computer apparatus automatically generates a respective filter  175  for filtering purchase related electronic messages ( FIG. 7 , block  176 ). 
     In the illustrated example, if a cluster is not assigned a respective purchase related label ( FIG. 7 , block  174 ), the computer apparatus proceeds directly to process the next sample i=i+1 of electronic messages  164  for the next cluster of headers  160  ( FIG. 7 , block  177 ). In this process, the computer apparatus repeats the cluster labeling process based on the classification of the constituent electronic messages in the next sample i=i+1 ( FIG. 7 , blocks  166 - 172 ). 
     In an alternative example, instead of proceeding directly to process the next sample i=i+1 of electronic messages  164  ( FIG. 7 , block  177 ), the computer apparatus automatically generates a respective filter  179  for filtering non-product-purchase related electronic messages ( FIG. 7 , block  178 ) for each cluster that is not assigned a respective purchase related label. In some of these examples, the non-product-purchase related electronic message filters  179  are installed at the front-end of the message filter building system  118 , either as a component of the header sampler  120  (as shown in  FIG. 7 ) or as part of a separate pre-filter. The non-product-purchase related electronic message filters  179  are used to filter-out headers of non-product-purchase related electronic messages that are fetched by the header sampler  120 . In this way, electronic messages with headers that correspond to previously identified non-product-purchase related electronic messages can be filtered out to further reduce the processing resources, data storage resources, network resources, and production times needed to build purchase related electronic message filters. 
       FIG. 10  shows an example of a message filter building system  180  that incorporates elements of the message filter building system  118  of  FIG. 7 , and additionally implements an iterative process for building filters from samples of the fetched header data. 
     In this example, the header sampler  120  fetches, for each of one or more senders, a respective sample of the headers in the electronic message population that are associated with the sender and stored on one or more of the network data storage systems  122 - 126  across multiple user accounts. In other examples, the header sampler  120  fetches a sample of headers across sender domains. The pre-processor  128  pre-processes the subject fields in the fetched sample of electronic message headers before the headers are grouped into clusters. The cluster engine  130  groups the pre-processed headers into clusters  160  based on a density based clustering process that correlates the clusters with respective dense regions in a clustering data space in which the pre-processed headers are separated from one another based on similarities between respective pairs of the pre-processed headers. For each set i of header clusters  160  that is assigned a respective purchase related label, the computer apparatus automatically generates a respective set i of filters for filtering purchase related electronic messages in accordance with the method described above in connection with  FIG. 7  (see, e.g.,  FIG. 7 , block  176 ). 
     In the first iteration of the filter building process, the message filter building system  180  builds a respective first set of filters (i.e., {filter set i}) for each sender from a respective first sample of the headers that are associated with the sender. 
     The process is repeated for a respective second sample of headers in the electronic message population for each sender. In this second iteration of the filter building process, the message filter building system  180  builds a respective second set of filters (i.e., {filter set i+1}) for each sender from a respective second sample of the headers that are associated with the sender. 
     The filter results are compared on a per sender basis ( FIG. 10 , block  182 ). In this process, for each sender, the computer apparatus retrieves a respective set of all the headers in the population that correspond to the sender ( FIG. 10 , block  183 ). The respective first and second sets of filters (i.e., {filter set i} and {filter set i+1}) for the sender are then applied to the respective set all the headers in the population that correspond to the sender to produce {filter results i} and [filter results i+1}. 
     If the filtering results are similar ( FIG. 10 , block  184 ), the filter building process ends ( FIG. 10 , block  186 ). In some examples, the similarity between the first and second filtering results is determined based on a comparison of the respective numbers of the retrieved headers in the complete set of headers that are not matched to any filter in the first and second sets of filters. If the numbers of headers that are unmatched by the first and second sets of filters are similar, the filter sets are deemed to be sufficiently similar and the filter building process stops ( FIG. 10 , block  186 ). 
     If the filter results are not similar ( FIG. 10 , block  184 ), the filter building process continues as follows. In some examples, filters that are shared between the compared filter sets are saved in memory  188  for use in filtering electronic messages ( FIG. 10 , block  190 ). The previous header sample size is increased ( FIG. 10 , block  192 ), and another iteration of the filter building process is performed ( FIG. 10 , block  194 ) using the larger respective sample of headers for each sender. 
       FIG. 11  shows a process for generating a respective filter for a cluster  198  of headers. In some examples, the computer apparatus performs this process for each purchase related cluster (e.g., each cluster that is labeled with a purchase related label) ( FIG. 11 , block  200 ). The computer apparatus counts the total number of times each bigram appears in the subject lines of all the headers in the cluster  198  ( FIG. 11 , block  202 ). The computer apparatus selects a header from the cluster  198  ( FIG. 11 , block  204 ). For each bigram in the subject field of the selected header, the computer apparatus determines a respective measure of frequency with which the bigram appears in the subject fields of the headers ( FIG. 11 , block  206 ). Examples of such frequency measures include a ratio that measures the number of subject fields that contain the bi-gram divided by the number of subject fields that do not contain the bigram, a proportion that measures the number the subject fields that contain the bigram divided by the total number of subject fields, and a rate that measures the frequency with which a subject field containing the bigram appears in the subject fields. The computer apparatus builds a filter for the cluster by incorporating each of the bigrams in the selected header that is associated with a respective frequency measure that satisfies a threshold (e.g., 80%) ( FIG. 11 , block  208 ). The computer apparatus determines if the set of bigrams that have been incorporated into the filter for the cluster has converged ( FIG. 11 , block  210 ). In some examples, the set of bigrams is determined to have converged if the set of bigrams did not change in the last iteration. If the set of bigrams has converged ( FIG. 11 , block  210 ), the bigrams in the set are converted into a filter for the cluster ( FIG. 11 , block  212 ). In some examples, the bigrams are converted into one or more regular expressions that define the filter. If the set of bigrams has not converged ( FIG. 11 , block  210 ), the process is repeated for another header selected from the cluster  198  ( FIG. 11 , blocks  204 - 210 ). 
     In other examples of the filter building process of  FIG. 11 , instead of using bigrams, the analysis of the header subject fields is performed with respect to other textual characteristics, including strings, n-grams, and words appearing in the subject fields. 
     III. Exemplary Computer Apparatus 
     Computer apparatus are specifically programmed to provide improved processing systems for performing the functionality of the processes described herein. In some examples, the process of building a electronic message filter and the process of filtering electronic messages with one or more electronic message filters are performed by separate and distinct computer apparatus. In other examples, the same computer apparatus performs these processes. 
       FIG. 12  shows an example embodiment of computer apparatus that is implemented by a computer system  320 . The computer system  320  includes a processing unit  322 , a system memory  324 , and a system bus  326  that couples the processing unit  322  to the various components of the computer system  320 . The processing unit  322  may include one or more data processors, each of which may be in the form of any one of various commercially available computer processors. The system memory  324  includes one or more computer-readable media that typically are associated with a software application addressing space that defines the addresses that are available to software applications. The system memory  324  may include a read only memory (ROM) that stores a basic input/output system (BIOS) that contains start-up routines for the computer system  320 , and a random access memory (RAM). The system bus  326  may be a memory bus, a peripheral bus or a local bus, and may be compatible with any of a variety of bus protocols, including PCI, VESA, Microchannel, ISA, and EISA. The computer system  320  also includes a persistent storage memory  328  (e.g., a hard drive, a floppy drive, a CD ROM drive, magnetic tape drives, flash memory devices, and digital video disks) that is connected to the system bus  326  and contains one or more computer-readable media disks that provide non-volatile or persistent storage for data, data structures and computer-executable instructions. 
     A user may interact (e.g., input commands or data) with the computer system  320  using one or more input devices  330  (e.g. one or more keyboards, computer mice, microphones, cameras, joysticks, physical motion sensors, and touch pads). Information may be presented through a graphical user interface (GUI) that is presented to the user on a display monitor  332 , which is controlled by a display controller  334 . The computer system  320  also may include other input/output hardware (e.g., peripheral output devices, such as speakers and a printer). The computer system  320  connects to other network nodes through a network adapter  336  (also referred to as a “network interface card” or NIC). 
     A number of program modules may be stored in the system memory  324 , including application programming interfaces  338  (APIs), an operating system (OS)  340  (e.g., the Windows® operating system available from Microsoft Corporation of Redmond, Wash. U.S.A.), software applications  341  including one or more software applications programming the computer system  320  to perform one or more of the process of building an electronic message filter and the process of filtering electronic messages with an electronic message filter, drivers  342  (e.g., a GUI driver), network transport protocols  344 , and data  346  (e.g., input data, output data, program data, a registry, and configuration settings). 
     IV. Conclusion 
     The embodiments described herein provide improved systems, methods, and computer-readable media for building purchase related electronic message filters and filtering purchase related electronic messages. 
     Other embodiments are within the scope of the claims.