Abstract:
In general, this disclosure describes techniques of enabling devices to download only current portions of email messages without downloading historical portions of the email messages. For instance, when an email client generates a reply email message to an original email message, the reply email message includes a current portion and a historical portion. The current portion of the reply email message includes new information and the historical portion of the reply email message includes the original email message. The techniques of this disclosure enable devices to download the current portions of email messages without downloading the historical portions of the email messages.

Description:
BACKGROUND 
     Wireless handheld devices have become popular tools to check and send email messages because mobile wireless handheld devices can be used from practically anywhere. This makes wireless handheld devices ideal for businesspeople that are frequently away from their office computers, but need to stay in contact with their associates and clients. 
     However, wireless handheld devices can have several known shortcomings. These shortcomings include slow data transmission rates and limited battery lives. Moreover, wirelessly transmitting data consumes considerable amounts of energy, thereby further shortening the battery lives of wireless handheld devices. Consequently, sending and receiving lengthy email messages may quickly drain the batteries of wireless handheld devices. 
     SUMMARY 
     In general, this disclosure describes techniques of enabling devices to download only current portions of email messages without downloading historical portions of the email messages. For instance, when an email client generates a reply email message to an original email message, the reply email message includes a current portion and a historical portion. The current portion of the reply email message includes new information and the historical portion of the reply email message includes the original email message. The techniques of this disclosure enable devices to download the current portions of email messages without downloading the historical portions of the email messages. 
     In some, but not necessarily all, circumstances, downloading the current portions of email messages without downloading the historical portions of the email messages may result in faster access to the current portions of the email messages. In addition, in some, but not necessarily all, circumstances, downloading the current portions of email messages without downloading the historical portions of the email messages may result in less energy consumption because energy is not consumed to download the historical portions of the email messages. 
     The techniques of this disclosure may be conceptualized in many ways. For example, the techniques of this disclosure may be conceptualized as a method that comprises receiving, at a server, an original email message that is a child email message of a second email message, the original email message including a current portion and a historical portion, the current portion containing content not in the second email message and the historical portion containing a copy of the second email message. The method also comprises generating, at the server, a truncated email message that includes the current portion of the original email message and not the historical portion of the original email message. In addition, the method comprises transmitting the truncated email message. 
     In another example, the techniques of this disclosure may be conceptualized as a computer-readable medium that comprises instructions that, when executed by a device, cause the device to receive an incoming truncated email message associated with a first email message this is a child email message of a second email message, the first email message including a current portion and a historical portion, the current portion containing content not in the second email message and the historical portion containing a copy of the second email message, the incoming truncated email message including the current portion of the first email message and excluding the historical portion of the first email message. The instructions also cause the device to recover, after reception of the incoming truncated email message, the first email message. In addition, the instructions cause the device to cause a presentation device to present the first message. 
     In another example, the techniques of this disclosure may be conceptualized as a communication system that comprises a first email server, a second email server, a first client device, a second client device, and a network that facilitates communication between the first email server, the second email server, the and the first client device. The first client device comprises a network interface that enables the sending client device to send data on the network. In addition, the first client device comprises an incoming message module that receives a first email message. Furthermore, the first client device comprises an interface presentation module that receives a command from a user to send a second email message that includes a current portion and a historical portion that includes the first email message. The second email message is related to the first email message by a relationship selected from a group consisting of: (i) the second email message is a reply to the first email message; and (ii) the second email message is a forward of the first email message. The first client device also comprises an outgoing message module that includes a “portion partition” header field that indicates a start of the historical portion of the second email message. In addition, the first client device comprises a transmission module that causes the network interface of the first client device to send the second email message to the first email server via the network. The first email server sends the second email message to the second email server. The second email server comprises a network interface that enables the second email server to receive data from the network and to send data on the network. The second email server also comprises an incoming message module that receives the second email message. In addition, the second email server comprises a truncation module that (1) determines whether the second email message includes the “portion partition” header field; and (2) generates, when it is determined that the second email message includes the “portion partition” header field, a truncated email message that includes all of the second email message prior to the start of the historical portion of the second email message. The second email server also comprises a transmission module that causes the network interface of the second email server to forward the truncated email message to the second client device. The second client device comprises a presentation device that is capable of displaying data. The second client device also comprises a message cache that is capable of storing email messages. In addition, the second client device comprises an incoming message module that receives the truncated email message and stores the truncated email message in the message cache. Moreover, the second client device comprises an interface presentation module that causes the presentation device to present an interface that displays the truncated email message. In addition, the second client device comprises a message recovery module that: (i) determines whether the truncated email message includes a reference header field that specifies a message identifier; (ii) determines, when it is determined that the truncated email message includes the reference header field that specifies the message identifier, whether the message cache stores an email message that includes a message identifier header field that specifies a message identifier that is equal to the message identifier specified by the reference header field of the truncated email message; (iii) appends, when it is determined that the message cache stores the email message that includes the message identifier header field that specifies the message identifier that is equal to the message identifier specified by the reference header field of the truncated email message, the stored email message to the truncated email message, thereby reassembling the second email message; (iv) sends, when it is determined that the message cache does not store the email message that includes the message identifier header field that specifies the message identifier that is equal to the message identifier specified by the reference header field of the truncated email message or when it is determined that the truncated email message does not include the reference header field that specifies the message identifier, a request for the second email message; and (v) receives, in response to the request for the second email message, the second email message. After the message recovery module recovers the second email message, the interface presentation module causes the presentation device to display the second email message. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating an example communication system. 
         FIG. 2  is a block diagram illustrating example details of the intermediate email server illustrated in the example of  FIG. 1 . 
         FIG. 3  is a flowchart illustrating an example operation of an email server application executing in the example intermediate email server of  FIG. 2 . 
         FIG. 4  is a flowchart illustrating an example operation of a truncation module in the email server application executing in the example intermediate email server of  FIG. 2 . 
         FIG. 5  is a block diagram illustrating example details of the receiving client device illustrated in the example of  FIG. 1 . 
         FIG. 6  is a flowchart illustrating an example operation to recover an original email message. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a block diagram illustrating an example communication system  2 .  FIG. 1  is provided for explanatory purposes only and is not intended to represent a sole way of implementing the techniques of this disclosure. Rather, many other implementations of these techniques are possible. 
     As illustrated in the example of  FIG. 1 , communication system  2  includes a client device  4 A and a client device  4 B. Client device  4 A and client device  4 B may be a wide variety of different types of devices. For example, client device  4 A and/or client device  4 B may be personal computers, mobile telephones, personal media players, smart phones, television set-top boxes, personal digital assistants, devices integrated into vehicles, mainframe computers, computer workstations, standalone servers, server blades, server farms, game platforms, or one or more other types of devices. A user  8  may use client device  4 A and a user  10  may use client device  4 B. 
     Furthermore, as illustrated in the example of  FIG. 1 , communication system  2  includes a sending email server  12 , an intermediate email server  14 , and a receiving email server  16 . Sending email server  12 , intermediate email server  14 , and receiving email server  16  may be a variety of different types of devices. For instance, sending email server  12 , intermediate email server  14 , and/or receiving email server  16  may be standalone servers, server blades, server farms, personal computers, or other types of devices. Furthermore, it should be appreciated that the functionality of one or more of sending email server  12 , intermediate email server  14 , and/or receiving email server  16  may be performed by a single physical device. Moreover, in some implementations, no logical distinction is drawn between sending email server  12 , intermediate email server  14 , and/or receiving email server  16 . 
     Communication system  2 , in the example of  FIG. 1 , includes a network  18 . Network  18  may be one of many different types of network. For instance, network  18  may be a local area network, a wide area network (e.g., the Internet), a global area network, a metropolitan area network, or another type of network. Network  18  may include many network devices and many network links. The network devices in network  18  may include bridges, hubs, switches, firewalls, routers, load balancers, and other types of network devices. The network links in network  18  may include wired links (e.g., coaxial cable, fiber optic cable, 10BASE-T cable, 100BASE-TX cable, etc.) and may include wireless links (e.g., WiFi links, WiMax links, wireless broadband links, mobile telephone links, Bluetooth links, infrared links, etc.). 
     User  8  may use client device  4 A to send email messages. For example, client device  4 A may execute an instance of a Microsoft OUTLOOK® messaging and collaboration client that enables user  8  to send and receive email messages. In another example, client device  4 A may execute a web browser (e.g., Microsoft INTERNET EXPLORER® internet browser, Mozilla Firefox internet browser, Apple Opera internet browser, etc.) that presents an online email interface that enables user  8  to send and receive email messages. 
     When user  8  uses client device  4 A to send an email message, client device  4 A may send the email message to sending email server  12 . Sending email server  12  may execute a mail transfer agent, such as Microsoft Exchange Server, a Simple Mail Transfer Protocol (SMTP) agent, or another type of mail transfer agent. For instance, when sending email server  12  executes a SMTP agent and the SMTP agent receives the email message, sending email server  12  may extract a domain name from an email address of a recipient of the email message. The mail transfer agent may then use a Domain Name System (DNS) to find Internet Protocol (IP) addresses of recipient mail transfer agents associated with the domain name. After finding an IP address of the recipient mail transfer agent, the SMTP agent may initiate a Transmission Control Protocol (TCP) session with the recipient mail transfer agent and use this TCP session to send the email message to the recipient transfer agent. 
     Intermediate email server  14  executes an instance of a mail transfer agent that accepts email message that specify email addresses that include a given domain name. For example, intermediate email server  14  may accept email messages that specify email addresses that include the domain name “example.com”. In this example, when sending email server  12  receives an email message that specifies the email address “smith@example.com”, sending email server  12  may send the email message to intermediate email server  14 . 
     When intermediate email server  14  receives the email message (i.e., the original email message), intermediate email server  14  generates a truncated email message. The truncated email message is an email message that includes a current portion of the original email message and excludes a historical portion of the original email message. 
     As used in this disclosure, a first email message includes a current portion and a historical portion when the first email message is a child email message of a second email message. A child email message is an email message that is a reply to or a forward of another email message. The historical portion of the first email message contains a copy of the second email message and the current portion of the first email message contain content that is not in the second email message. It should be noted that the second email message may itself be a child email message of a third email message and may include a copy of the third email message as a historical portion. Consequently, the historical portion of the first email message may include a copy of the second email message and a copy of the third email message. For example, in the following email message, the portion above the first dashed line is the current portion of the email message and the portion below the first dashed line is the historical portion of the email message. 
     
       
         
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 From: Kelly 
               
               
                   
                 Sent: Monday, March 03, 2008 11:42 AM 
               
               
                   
                 To: Justin 
               
               
                   
                 Subject: RE: RE: Lunch? 
               
               
                   
                 Let&#39;s go to Mario&#39;s at 12:30 
               
               
                   
                 ----------------------------------------------- 
               
               
                   
                   From: Justin 
               
               
                   
                   Sent: Monday, March 03, 2008 11:42 AM 
               
               
                   
                   To: Kelly 
               
               
                   
                   Subject: RE: Lunch? 
               
               
                   
                   Sure. Where do you want to go? 
               
               
                   
                 ----------------------------------------------- 
               
               
                   
                     From: Kelly 
               
               
                   
                     Sent: Monday, March 03, 2008 11:38 AM 
               
               
                   
                     To: Justin 
               
               
                   
                     Subject: Lunch? 
               
               
                   
                     Do you want to get lunch today? 
               
               
                   
                   
               
             
          
         
       
     
     As described in detail below, intermediate email server  14  may determine how to generate the truncated email message in a variety of ways. For example, the original email message may include a “portion partition” header field that indicates a start of the historical portion of the original email message. The “portion partition” header field may be one of the header fields of the original email message. In this example, intermediate email server  14  may use this “portion partition” header field to truncate all bytes of the original email message after the last byte of the current portion of the original email message, thereby generating the truncated email message. After intermediate email server  14  generates the truncated email message, intermediate email server  14  may forward the truncated email message to receiving email server  16 . 
     When receiving email server  16  receives the truncated email message, receiving email server  16  may enable client device  4 B to retrieve the truncated email message. Receiving email server  16  may enable client device  4 B to retrieve the truncated email message in a variety of ways. For example, receiving email server  16  may enable client device  4 B to receive the truncated email message wirelessly. In this example, receiving email server  16  may execute an instance of BlackBerry Enterprise Server produced by Research In Motion, Inc. of Waterloo, Ontario. Furthermore, in this example, the instance of BlackBerry Enterprise Server may push the truncated email message to client device  4 B, which may be a wireless handheld device. In another example, receiving email server  16  may execute an instance of a Microsoft Exchange Server mail transfer agent that alerts an instance of Microsoft OUTLOOK® messaging and collaboration software executing on client device  4 B that the truncated email message is available for retrieval. In response to such an alert, the instance of Microsoft OUTLOOK® messaging and collaboration software may retrieve the truncated email message. 
     Upon receiving the truncated email message, client device  4 B may present the truncated email message to user  10 . For instance, client device  4 B may present a user interface that contains the truncated email message. In other instances, when client device  4 B receives the truncated email message, client device  4 B may dynamically recover the original email message. As described in detail below, client device  4 B may dynamically recover the original email message in variety of ways. 
       FIG. 2  is a block diagram illustrating example details of intermediate server  14 .  FIG. 2  is provided for explanatory purposes and is not meant to represent a sole way of implementing intermediate email server  14 . Furthermore, for ease of understanding, actual implementations of intermediate email server  14  may include many additional features that are not illustrated in the example of  FIG. 2 . For instance, an actual implementation of intermediate email server  14  would include a power distribution system, a cooling system, and so on. 
     As illustrated in the example of  FIG. 2 , intermediate email server  14  includes a bus  30  that logically represents one or more buses that facilitate data communication between a processor  32 , a data storage medium  34 , and a network interface  36 . For instance, bus  30  may represent a HyperTransport bus, an InfiniBand bus, a peripheral component interconnect (PCI) express bus, a universal serial bus (USB), or another type of bus. 
     In the example of  FIG. 2 , data storage medium  34  represents a logical collection of one or more volatile and/or non-volatile data storage media that are capable of storing data, including software instructions and application data. For instance, data storage medium  34  may represent one or more magnetic disks, optical discs, flash memory units, dynamic random access memory (RAM) units, RamBus RAM units, synchronous dynamic RAM units, or other types of data storage media. 
     Processor  32  is an integrated circuit that is capable of executing instructions. For example, processor  32  may be a microprocessor, an application-specific integrated circuit, a digital signal processor, a graphics processing unit, or another type of integrated circuit that is capable of executing instructions. For instance, processor  32  may be a Core processor manufactured by Intel Corporation of Santa Clara, Calif., or a K10 processor manufactured by Advanced Micro Devices, Inc. of Sunnyvale, Calif. Although not illustrated in the example of  FIG. 2 , intermediate email server  14  may include several such processors. Processor  32  may read data stored in data storage medium  34  by retrieving the data via bus  30 . Moreover, processor  32  may write data to data storage medium  34  by sending the data to data storage medium  34  via bus  30 . 
     Network interface  36  enables intermediate email server  14  to send data on network  18  and to receive data from network  18 . For instance, network interface  36  may be an Ethernet network interface, a token ring network interface, a fiber optic network interface, a WiFi network interface, a WiMax network interface, or another type of wired or wireless network interface. When network interface  36  receives data from network  18 , network interface  36  may store the data in data storage medium  34  by sending the data to data storage medium  34  via bus  30 . Furthermore, processor  32  may send data via bus  30  to network interface  36  for transmission on network  18 . 
     As illustrated in the example of  FIG. 2 , data storage medium  34  stores an operating system  38 . For instance, data storage medium  34  may store a WINDOWS SERVER® operating system or a WINDOWS VISTA® operating system from Microsoft Corporation, a UNIX operating system, an OS X® operating system from Apple Inc. of Cupertino, Calif., a Linux operating system, or another type of operating system. When executed by processor  32 , operating system  38  manages the sharing of resources of intermediate email server  14  and provides interfaces that other software applications can use to access those resources. For instance, a software application can use an interface provided by operating system  38  to send data through network interface  36  to network  18 . 
     Furthermore, as illustrated in the example of  FIG. 2 , data storage medium  34  stores an email server application  40 . When executed by processor  32 , email server application  40  receives incoming email messages from network  18  and sends outgoing email messages to other email servers via network  18 . 
     Email server application  40  may be subdivided into an incoming message module  42 , a truncation module  44 , a message retrieval module  46 , and a message retrieval module  52 . It should be appreciated that incoming message module  42 , truncation module  44 , message retrieval module  46 , and message retrieval module  52  may share one or more common instructions. Furthermore, it should be appreciated that email server application  40  may include other modules in addition to incoming message module  42 , truncation module  44 , message retrieval module  46 , and message retrieval module  52  and provide functionality in addition to the functionality provided by incoming message module  42 , truncation module  44 , message retrieval module  46 , and message retrieval module  52 . For instance, email server application  40  may include a module that filters out “spam” email messages. 
     When executed by processor  32 , incoming message module  42  interacts with operating system  38  to receive incoming email messages that are received from network  18  by network interface  36 . For instance, incoming message module  42  may use an interface provided by operating system  38  to configure a callback that causes operating system  38  to provide incoming email messages to incoming message module  42 . When incoming message module  42  receives an incoming email message, incoming message module  42  may perform one or more email processing operations on the incoming email message. For instance, incoming message module  42  may determine whether the incoming email address includes a “to” header field, a “cc” header field, or a “bcc” header field that specifies an email address associated with an active account maintained by intermediate email server  14 . In this example, incoming message module  42  may generate an outgoing “bounce” message when the “to” header field, the “cc” header field, or the “bcc” header field of the incoming email message specifies an email address associated with an inactive account that was previously maintained by intermediate email server  14 . 
     After incoming message module  42  performs the email processing operations on the incoming email message, incoming message module  42  may store the incoming email message in a message database  50 . Message database  50  may be a variety of different types of database. For instance, message database  50  may be a relational database, a file system, a file, an associative database, an object-oriented database, or another type of database. Storing the incoming email message in message database  50  may enable the incoming email message to be retrieved multiple times. After storing the incoming email message in message database  50 , incoming message module  42  may provide the incoming email message to truncation module  44 . 
     When executed by processor  32 , truncation module  44  receives the incoming email message from incoming message module  42  and automatically generates a truncated email message that includes a current portion of the incoming email message and not the historical portion of the original email message. In some implementations, truncation module  44  may include a “truncated” header field in the truncated email message to indicate that the truncated email message is a truncation. An example operation of truncation module  44  is provided below with reference to  FIG. 4 . 
     After truncation module  44  generates the truncated email message, truncation module  44  may provide the truncated email message to transmission module  46 . Upon receiving the truncated email message, transmission module  46  may use one or more software interfaces provided by operating system  38  to cause network interface  36  to send the truncated email message to receiving email server  16  for eventual delivery to client device  4 B. It should be appreciated that in some implementations, the functionality of receiving email server  16  is merged into intermediate email server  14 . In these implementations, transmission module  46  may use software interfaces provided by operating system  38  to cause network interface  36  to send the truncated email message directly to client device  4 B. 
     In addition, when processor  32  executes message retrieval module  52 , message retrieval module  52  may receive requests for original email messages. In response to a request for an original email message, message retrieval module  52  may search message database  50  for the original email message. When message retrieval module  52  identifies the original email message, message retrieval module  52  provides the original email message to transmission module  46 . Upon receiving the original email message from message retrieval module  52 , transmission module  46  may use operating system  38  to send the original email message to receiving email server  16  or client device  4 B, depending on how communication system  2  is configured. In an alternate implementation, message retrieval module  52  may cause transmission module  46  to send only the historical portion of the original email message to receiving email server  16 . When client device  4 B receives the historical portion of the original email message, client device  4 B may append the historical portion of the original email message to the truncated email message, thereby recovering the original email message. 
     Message retrieval module  52  may receive a request for an original email message for a variety of reasons. For example, client device  4 B may receive a truncated email message that includes the current portion of the original email message, but not the historical portion of the original email message. In this example, user  10  of client device  4 B may not immediately understand the context of the truncated email message without being able to read the historical portion of the original email message. Consequently, in this example, user  10  may instruct receiving client device  8  to request the original email message. When receiving client device  8  receives the original email message, receiving client device  8  may replace the truncated email message with the original email message. 
     As explained below, it should be appreciated that in some implementations, receiving client device  8  may use locally stored information to recover the original email message without sending a request for the original email message. In these implementations, message retrieval module  52  may be unnecessary. 
       FIG. 3  is a flowchart illustrating an example operation of email server application  40 . As illustrated in the example of  FIG. 3 , incoming message module  42  in email server application  40  receives an incoming email message ( 70 ). After incoming message module  42  receives the incoming email message, incoming message module  42  may store the incoming email message in message database  50  ( 72 ). 
     Next, truncation module  44  performs a truncation process on the incoming email message ( 74 ). An example truncation process is illustrated below with regard to  FIG. 4 . During the truncation process, truncation module  44  may generate a truncated email message that includes a current portion of the incoming email message and not a historical portion of the original email message. It should be appreciated that the email message that results from the truncation process may be the same as the incoming email message when the incoming email message does not include a historical portion. Furthermore, in some implementations, the email message that results from the truncation process may be the same as the incoming email message when the truncation process determines that removal of the historical portion of the incoming email message would be unnecessary or inappropriate. 
     After truncation module  44  performs the truncation process, transmission module  46  may cause network interface  36  to transmit the email message that results from the truncation process ( 76 ). 
       FIG. 4  is a flowchart illustrating an example operation of truncation module  44 . As illustrated in the example of  FIG. 3 , truncation module  44  may receive an original email message from incoming message module  42  ( 90 ). 
     After receiving the original email message, truncation module  44  may determine whether the original email message includes a “portion partition” header field that identifies a start of a historical portion of the original email message ( 92 ). The “portion partition” header field may identify a start of the historical portion of the original email message in a variety of ways. For instance, the “portion partition” header field may identify a start of the historical portion of the original email message by indicating how many bytes are in the current portion of the original email message. In another instance, the “portion partition” header field may identify the last byte of the current portion of the original email message by indicating how many bytes are in the historical portion of the original email message. 
     If truncation module  44  determines that the original email message includes a “portion partition” header field (“YES” of  92 ), truncation module  44  may determine whether the “portion partition” header field indicates that the original message includes a historical portion ( 94 ). In one example implementation, truncation module  44  may determine that the “portion partition” header field indicates that the original message includes a historical portion when the “portion partition” header field does not indicate a null value. If truncation module determines that the “portion partition” header field indicates that the original email message does not include a historical portion (“NO” of  94 ), truncation module  44  may output the original email message to transmission module  46  ( 96 ). 
     If truncation module  44  determines that the original email message does not include a “portion partition” header field (“NO” of  92 ), truncation module  44  may determine whether the original email message includes a string indicative of a start of a historical portion of the original email message ( 98 ). The string may be a block of one or more characters that identifies recipients, a sent time, a sender, and a subject. For instance, consider the following original email message: 
                                             From: Justin           Sent: Monday, March 03, 2008 11:42 AM           To: Kelly           Subject: RE: Lunch?           Sure. Let&#39;s go to Mario&#39;s at 12:30.           -----------------------------------------------             From: Kelly             Sent: Monday, March 03, 2008 11:38 AM             To: Justin             Subject: Lunch?             Do you want to get lunch today?                        
In this example, the string “From: Kelly Sent: Monday, March 3, 2008 11:38 AM To: Justin Subject: Lunch?” is indicative of the start of the historical portion of the original email message. In another instance, client device  4 A may be configured to automatically insert a string of one or more visible or invisible characters in the original email message that always indicate an end of the current portion of the original email message and the beginning of the historical portion of the original email message.
 
     If truncation module  44  determines that the original email message does not include a string indicative of the start of a historical portion of the original email message (“NO” of  98 ), truncation module  44  may output the original email message to transmission module  46  ( 96 ). 
     If truncation module  44  determines that the original email message includes a string indicative of the start of a historical portion of the original email message (“YES” of  98 ) or if truncation module  44  determines that the “portion partition” header field of the original email message indicates that the original email message includes a historical portion (“YES” of  94 ), truncation module  44  may generate a truncated email message that includes the current portion of the original email message, but not the historical email portion of the original email message ( 100 ). When truncation module  44  generates the truncated email message, truncation module  44  may include a “truncation” header field in the truncated email message that indicates that the truncated email message is a truncation of an original email message. After generating the truncated email message, truncation module  44  may output the truncated email message to transmission module  46  ( 102 ). 
     It should be appreciated that the operation illustrated in  FIG. 4  is provided as one example operation of truncation module  44  among many possible operations. For instance, some operations of truncation module  44  may not use a string to identify a start of a historical portion of an original email message. Other operations of truncation module  44  may not use a “portion partition” header field. 
       FIG. 5  is a block diagram illustrating example details of client device  4 B. As illustrated in the example of  FIG. 5 , client device  4 B includes a bus  120  that facilitates data communication between a processor  122 , a data storage medium  124 , a network interface  126 , a presentation device  128 , and an input interface  129 . For instance, bus  120  may represent a HyperTransport bus, an InfiniBand bus, a peripheral component interconnect (PCI) express bus, a universal serial bus (USB), or another type of bus. 
     In the example of  FIG. 5 , data storage medium  124  represents a logical collection of one or more volatile and/or non-volatile data storage media that are capable of storing data, including software instructions and application data. For instance, data storage medium  34  may represent one or more magnetic disks, optical discs, flash memory units, dynamic random access memory (RAM) units, RamBus RAM units, synchronous dynamic RAM units, or other types of data storage media. 
     Processor  122  is an integrated circuit that is capable of executing instructions. For example, processor  32  may be a microprocessor, an application-specific integrated circuit, a digital signal processor, a graphics processing unit, or another type of integrated circuit that is capable of executing instructions. Processor  122  may read data stored in data storage medium  124  by retrieving the data via bus  120 . Moreover, processor  122  may write data to data storage medium  34  by sending the data to data storage medium  124  via bus  120 . 
     Network interface  126  enables client device  4 B to send data on network  18  and to receive data from network  18 . For instance, network interface  36  may be an Ethernet network interface, a token ring network interface, a fiber optic network interface, a WiFi network interface, a WiMax network interface, or another type of wired or wireless network interface. When network interface  126  receives data from network  18 , network interface  126  may store the data in data storage medium  124  by sending the data to data storage medium  124  via bus  120 . Furthermore, processor  122  may send data via bus  120  to network interface  126  for transmission on network  18 . 
     Presentation interface  128  enables client device  4 B to output data to be presented on a presentation device  130 . For instance, presentation device  130  may be a monitor and presentation interface  128  enables client device  4 B to output data to be displayed on this monitor. In another instance, presentation device  130  may be a speaker and presentation interface  128  enables client device  4 B 0  to output data to be played on the speaker. 
     Input interface  129  enables client device  4 B to receive user input from an input device  131 . Input device  131  may be a wide variety of different types of user input devices. For instance, input device  131  may be a keyboard, a mouse, a touch-sensitive screen, a microphone, a button array, a trackball, an electronic drawing pad, a gaming controller, or another type of input device. 
     As illustrated in the example of  FIG. 5 , data storage medium  124  stores an operating system  132 . For instance, data storage medium  124  may store a WINDOWS VISTA® operating system from Microsoft Corporation, a UNIX operating system, an Apple OS X® operating system, a Linux operating system, or another type of operating system. When executed by processor  122 , operating system  132  manages the sharing of resources of client device  4 B and provides software interfaces that other software applications can use to access those resources. 
     Furthermore, as illustrated in the example of  FIG. 5 , data storage medium  124  stores an email client application  134 . When executed by processor  122 , email client application  134  receives incoming email messages from receiving email server  16  via network  18  and sends outgoing email messages to receiving email server  16  via network  18 . 
     Email client application  134  may be subdivided into an incoming message module  136 , a message recovery module  138 , an interface presentation module  140 , an outgoing message module  142 , and a transmission module  144 . It should be appreciated that the illustrated modules of email client application  134  may share one or more common instructions. Furthermore, it should be appreciated that email client application  134  may include other modules in addition to the illustrated modules and provide functionality in addition to the functionality provided by the illustrated modules. 
     When executed by processor  122 , incoming message module  136  receives incoming email messages from receiving email server  16 . In one example implementation, incoming message module  136  may use a software interface provided by operating system  132  to receive incoming email messages received by network interface  126 . Incoming message module  136  may receive incoming email messages that have been truncated and incoming email messages that are still in their original forms. Upon receiving an incoming email message, incoming message module  136  may store the incoming email message in a message cache  146 . 
     Interface presentation module  136 , when executed by processor  122 , uses one or more software interfaces provided by operating system  132  to cause presentation interface  128  to present a user interface on presentation device  130 . The user interface may be a wide variety of user interfaces. For instance, the user interface may be a graphical user interface, a command-line interface, or another type of user interface. The user interface may display email messages stored in message cache  146 . The user interface enables user  10  to read email messages stored in message cache  146 . 
     Prior to presenting an email message in the user interface, interface presentation module  136  may determine whether the email message is a truncated email message. Interface presentation module  136  may determine whether the email message is a truncated email message in a variety of ways. For example, interface presentation module  136  may determine that the email message is a truncated email message when the email message includes a “truncation” header field that indicates that the email message is a truncated email message. In a second example, interface presentation module  136  may determine that the email message is a truncated email message when the subject header field of the email message includes a prefix that indicates that the email message is a reply to or a forward of an earlier email message and when the email message does not include a string that is indicative of the start of a historical portion of an email message. 
     When interface presentation module  136  determines that the email message is a truncated email message, interface presentation module  136  may be configured to do one of several things. For example, interface presentation module  136  may be configured to automatically instruct message recovery module  138  to recover an original email message of the truncated email message. In a second example, interface presentation module  140  may be configured to present an icon in the user interface that, when selected by user  10  using input device  131 , causes interface presentation module  140  to instruct message recovery module  138  to recover an original email message of the truncated email message. In a third example, interface presentation module  140  may be configured to instruct message recovery module  138  to recover an original email message of the truncated email message when user  10  uses input device  131  to scroll past a certain point in the truncated email message as presented in the user interface. 
     Message recovery module  138 , when executed by processor  122 , performs an operation to recover an original email message of a truncated email message. An example operation to recover the original email message is provided with reference to  FIG. 6 , below. After message recovery module  138  recovers the original email message, message recovery module  138  may replace the copy in message cache  142  of the truncated email message with the original email message. Interface presentation module  140  may then cause presentation module  128  to present the original email message on presentation device  130 . 
     When executed by processor  122 , outgoing message module  142  enables user  10  to create a new outgoing email message. For instance, the user interface provided by interface presentation module  140  may include an icon or a command that, when selected, instructs interface presentation module  140  to present a user interface that enables user  10  to compose an outgoing email message. When user  10  is finished composing the outgoing email message and inputs a command to send the outgoing email message, outgoing message module  142  may determine whether the outgoing email message includes a current portion and a historical portion. User  10  may use input device  131  to input the command to send the outgoing email message. If the outgoing email message includes a current portion and a historical portion, outgoing message module  142  may include in the outgoing email message a “portion partition” header field that indicates a start of the historical portion of the outgoing email message. After outgoing message module  142  includes the “portion partition” header field in the outgoing email message, outgoing message module  142  may instruct transmission module  144  to send the outgoing email message to receiving email server  16 . 
     In some implementations, client device  4 A may execute an instance of email client application  134  and may send and receive email messages in the manner described above for client device  4 B. Furthermore, in some implementations, a web server may execute an instance of email client application  134 . In these implementations, the web server may also execute an instance of a web application that enables client device  4 B to send and receive email message through a web browser interface. 
       FIG. 6  is a flowchart illustrating an example operation to recover an original email message. In the example of  FIG. 6 , message recovery module  138  may originally receive a request for an original email message associated with a truncated email message received by client device  4 B ( 160 ). After message recovery module  138  receives the request for the original email message, message recovery module  138  may determine whether the truncated email message includes a reference header field that specifies a message identifier that identifies an earlier email message ( 162 ). A reference header field is a header field of an email message that defines a relationship with another email message. For instance, Internet Engineering Task Force (IETF) Request For Comment (RFC) 2822 specifies that email messages may include “in-reply-to” header fields and “references” header fields that specify message identifiers of other email messages. 
     If message recovery module  138  determines that the truncated email message specifies a message identifier that identifies an earlier email message (“YES” of  162 ), message recovery module  138  may determine whether message cache  146  stores an email message that specifies the message identifier ( 164 ). For instance, message recovery module  138  may determine whether any email message in message cache  146  includes a “message identifier” header field that specifies the message identifier specified by the “in-reply-to” header field of the truncated email message. 
     If message recovery module  138  determines that message cache  146  stores an email message that specifies the message identifier (“YES” of  164 ), message recovery module  138  may append the stored email message to the truncated email message, thereby reassembling the original email message ( 166 ). After appending the stored email message to the truncated email message, message recovery module  138  may replace the truncated email message with the recovered original email message ( 168 ). Interface presentation module  140  may then present the original email message on the user interface. 
     On the other hand, if message cache  146  does not store an email message that specifies the message identifier (“NO” of  164 ) or if the truncated email message does not specify a message identifier that identifies an earlier email message (“NO” of  162 ), message recovery module  138  may send a request for the original email message to receiving email server  16  ( 170 ). In response to the request, receiving email server  16  may send a request for the original email message to intermediate email server  14  ( 172 ). When intermediate email server  14  receives the request, message retrieval module  52  may retrieve the original email message from message database  50  ( 174 ). Upon retrieving the original email message, message retrieval module  52  may cause transmission module  46  to send the original email message to receiving email server  16  ( 176 ). When receiving email server  16  receives the original email message, receiving email server  16  sends the original email message to client device  4 B ( 178 ). Message recovery module  138  may then replace the truncated email message with the original email message ( 180 ). 
     The operation illustrated in the example of  FIG. 6  is merely one example operation among many possible operations to recover an original email message. For instance, other example operations may use other properties and characteristics of email messages to recover original email messages. 
     It is to be understood that the embodiments described herein may be implemented by hardware, software, firmware, middleware, microcode, or any combination thereof. When the systems and/or methods are implemented in software, firmware, middleware or microcode, program code or code segments, they may be stored in a machine-readable medium, such as a storage component. A code segment may represent a procedure, a function, a subprogram, a program, a routine, a subroutine, a module, a software package, a class, or any combination of instructions, data structures, or program statements A code segment may be coupled to another code segment or a hardware circuit by passing and/or receiving information, data, arguments, parameters, or memory contents. Information, arguments, parameters, data, etc. may be passed, forwarded, or transmitted using any suitable means including memory sharing, message passing, token passing, network transmission, etc. 
     For a software implementation, the techniques described herein may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes and instructions may be stored in computer-readable media and executed by processors. The memory unit may be implemented within the processor or external to the processor, in which case it can be communicatively coupled to the processor via various means as is known in the art. 
     Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.