Abstract:
A method, system, and computer program product for scanning emails by reducing the amount of decomposition processing that is performed to only the minimum necessary to fully scan the emails. This reduces the server resources needed, which improves server throughput and reduces costs. A method for processing email messages comprises the steps of receiving an email message comprising a plurality of items, scanning the email message with at least one scanner software, determining with each of the at least one scanner softwares what items of the plurality of items the email message is to be decomposed into, decomposing the email message to obtain the items determined by each of the at least one scanner software.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to scanning emails using a “scanner-driven” model, in which each scanner requests the amount of decomposition it requires to make a decision on the binary stream. 
         [0003]    2. Description of the Related Art 
         [0004]    The prevalence of unsolicited commercial email, commonly known as spam has grown rapidly and still growing. The corporate world and individual home users are spending millions of dollars to combat spam. Internet Service Providers (ISPs) have to cope with greatly increasing day-to-day amounts of network traffic due to the increase in spam emails. If spam traffic continues to grow, it may become unmanageable in the near future. 
         [0005]    Another common and growing problem is the spread of computer malwares. A typical computer malware is a program or piece of code that is loaded onto a computer and/or performs some undesired actions on a computer without the knowledge or consent of the computer operator. The most widespread, well-known and dangerous type of computer malware are computer viruses, that is, programs or pieces of code that replicate themselves and load themselves onto other connected computers. Once the virus has been loaded onto the computer, it is activated and may proliferate further and/or damage the computer or other computers. 
         [0006]    Typically, incoming emails may be scanned for a variety of undesirable contents. For example, emails may be scanned to determine whether or not they are spam, whether or not they include viruses or other malware, or whether or not they include inappropriate or other “bad” content. 
         [0007]    Typically, spam has been fought by the use of software that scans incoming email messages to determine whether each message is spam, includes malware, or includes bad content. If so, the messages are accordingly marked as ***SPAM*** or quarantined. When a data stream is presented for scanning it is often a compound object such as a MIME stream or archive file. This stream is decomposed into its constituent files before being presented to the AntiVirus, AntiSpam, bad conent, and other scanners. Traditionally this process has been “decomposition-driven”. That is, the binary stream is decomposed into as many different parts as possible and then each of these parts is been presented to the scanners. 
         [0008]    However, a large ISP can receive millions of emails each day, each of which must be scanned. Other large organizations may receive thousand of emails each day. On an average each mail takes from 15 milliseconds to 400 milliseconds to scan for such spam content. Thus consumes a huge amount of email server time and can in turn create a loss in the productivity of the organization. 
       SUMMARY OF THE INVENTION 
       [0009]    A method, system, and computer program product for scanning emails by reducing the amount of decomposition processing that is performed to only the minimum necessary to fully scan the emails. This reduces the server resources needed, which improves server throughput and reduces costs. This provides an alternative “scanner-driven” model, in which each scanner requests the amount of decomposition it requires to make a decision on the binary stream and no more, thus optimizing the amount of decomposition carried out for any one scan. Such a model is particularly relevant to AntiSpam scanning, where a decision can often be made before all possible levels of decomposition have been carried out. In more general terms it is applicable when users have turned off certain scanners, such as “content”. 
         [0010]    A method for processing email messages comprises the steps of receiving an email message comprising a plurality of items, scanning the email message with at least one scanner software, determining with each of the at least one scanner softwares what items of the plurality of items the email message is to be decomposed into, decomposing the email message to obtain the items determined by each of the at least one scanner software. 
         [0011]    The method may further comprise the step of scanning the items obtained by each of the at least one scanner softwares with that scanner software. The determining step may comprise the step of determining what items of the plurality of items the email message is to be decomposed into based on the items of the plurality of items that a scanner software is capable of scanning. The at least one scanner softwares may comprise a plurality of scanner softwares and the decomposing step may comprise the step of decomposing the email message to obtain each item determined by at least one of the plurality of scanner softwares only once. The method may further comprise the step of scanning the items obtained by at least one of the plurality of scanner softwares with that scanner software. The determining step may comprise the step of determining what items of the plurality of items the email message is to be decomposed into based on the items of the plurality of items that a scanner software is capable of scanning. The plurality of scanners may comprise at least one of an anti-virus scanner, an anti-spam scanner, and a bad content scanner. The plurality of items of the email message may comprise at least one of a MIME stream, MIME headers, an HTML item, a ZIP item, a text item, a document, and a list of URLs. The email messages may be incoming email messages or the email messages may be outgoing email messages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The details of the present invention, both as to its structure and operation, can best be understood by referring to the accompanying drawings, in which like reference numbers and designations refer to like elements. 
           [0013]      FIG. 1  is an exemplary block diagram of a system in which the present invention may be implemented. 
           [0014]      FIG. 2  is an exemplary block diagram of decomposition of a compound item, which is a MIME stream. 
           [0015]      FIG. 3  is an exemplary pseudo-code listing of a root function implementing scanner-driven decomposition. 
           [0016]      FIG. 4  is an exemplary pseudo-code listing of a scanner function implementing scanner-driven decomposition. 
           [0017]      FIG. 5  is an exemplary pseudo-code listing of a node function implementing scanner-driven decomposition. 
           [0018]      FIG. 6  is an exemplary pseudo-code listing of a node function implementing scanner-driven decomposition. 
           [0019]      FIG. 7  is an exemplary pseudo-code listing of a decomposer function implementing scanner-driven decomposition. 
           [0020]      FIG. 8  is an exemplary pseudo-code listing of a decomposer function implementing scanner-driven decomposition. 
           [0021]      FIG. 9  is an exemplary listing of scanners that may be used in implementing scanner-driven decomposition. 
           [0022]      FIG. 10  is an exemplary listing of decomposers that may be used in implementing scanner-driven decomposition. 
           [0023]      FIG. 11   a  is an exemplary block diagram of a first stage of decomposition of a compound item, which is a MIME stream. 
           [0024]      FIG. 11   b  is a diagram of a first stage of an example of scanner-driven decomposition. 
           [0025]      FIG. 12   a  is an exemplary block diagram of a second stage of decomposition of a compound item, which is a MIME stream. 
           [0026]      FIG. 12   b  is a diagram of a second stage of an example of scanner-driven decomposition. 
           [0027]      FIG. 13   a  is an exemplary block diagram of a third stage of decomposition of a compound item, which is a MIME stream. 
           [0028]      FIG. 13   b  is a diagram of a third stage of an example of scanner-driven decomposition. 
           [0029]      FIG. 14   a  is an exemplary block diagram of a fourth stage of decomposition of a compound item, which is a MIME stream. 
           [0030]      FIG. 14   b  is a diagram of a fourth stage of an example of scanner-driven decomposition. 
           [0031]      FIG. 15   a  is an exemplary block diagram of a fifth stage of decomposition of a compound item, which is a MIME stream. 
           [0032]      FIG. 15   b  is a diagram of a fifth stage of an example of scanner-driven decomposition. 
           [0033]      FIG. 16   a  is an exemplary block diagram of a sixth stage of decomposition of a compound item, which is a MIME stream. 
           [0034]      FIG. 16   b  is a diagram of a sixth stage of an example of scanner-driven decomposition. 
           [0035]      FIG. 17   a  is an exemplary block diagram of a second stage of decomposition of a compound item, which is a MIME stream. 
           [0036]      FIG. 17   b  is a diagram of a second stage of an example of scanner-driven decomposition. 
           [0037]      FIG. 18   a  is an exemplary block diagram of a third stage of decomposition of a compound item, which is a MIME stream. 
           [0038]      FIG. 18   b  is a diagram of a third stage of an example of scanner-driven decomposition. 
           [0039]      FIG. 19   a  is an exemplary block diagram of a fourth stage of decomposition of a compound item, which is a MIME stream. 
           [0040]      FIG. 19   b  is a diagram of a fourth stage of an example of scanner-driven decomposition. 
           [0041]      FIG. 20   a  is an exemplary block diagram of a fifth stage of decomposition of a compound item, which is a MIME stream. 
           [0042]      FIG. 20   b  is a diagram of a fifth stage of an example of scanner-driven decomposition. 
           [0043]      FIG. 21  is an exemplary block diagram of completed decomposition of a compound item, which is a MIME stream. 
           [0044]      FIG. 22  is an exemplary block diagram of completed decomposition of a compound item, which is a MIME stream. 
           [0045]      FIG. 23  is an exemplary block diagram of an email server, in which the present invention may be implemented. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0046]    A method, system, and computer program product for scanning emails reduces the server resources needed, which improves server throughput and reduces costs. This provides an alternative “scanner-driven” model, in which each scanner requests the amount of decomposition it requires to make a decision on the binary stream and no more, thus optimizing the amount of decomposition carried out for any one scan. Such a model is particularly relevant to AntiSpam scanning, where a decision can often be made before all possible levels of decomposition have been carried out. In more general terms it is applicable when users have turned off certain scanners, such as “content”. 
         [0047]    A block diagram of a system  100  in which the present invention may be implemented is shown in  FIG. 1 . Email server  102  receives email messages  104  via the Internet  106 , or other unsecure network. The email messages are processed by email scanner  108 . Email scanner  108  automates the highlighting, removal or filtering of e-mail spam, malware, and/or bad content by scanning through incoming and outgoing e-mails in search of traits typical of such undesirable items. Such scanning may include searching for patterns in the headers or bodies of messages. Each incoming email message is scanned to determine whether it is a dangerous spam email message, including malware or bad content, which is to be quarantined  110 , a spam email message that is to be marked as SPAM  112  and delivered to the recipients inbox  114 , or a clean email message  116  that is to be delivered as is to the recipient&#39;s inbox  114 . Email scanners  108  include a plurality of scanners  118 A-N, each of which is capable of scanning one or more different item types and scanning for one or more types of undesirable content. A scanner is a component that can run against an item to determine whether or not it has undesirable content, such as AntiVirus, AntiSpam, bad conent, and other scanners. An item is a stream of data and an item type is a category of item, such as a MICROSOFT WORD® document or a MICROSOFT WINDOWS® executable. A scannable item type is an item type that can be scanned by one or more scanners. Note that this can include compound items. An example is a MIME stream, which can be scanned by an AntiVirus scanner, an AntiSpam scanner, a bad conent scanner, and other scanners. An item of type unknown is an item of a type that cannot be established until the item has been decomposed. A compound item is an item that can be decomposed to one or more other items of type unknown. Example compound item types include zip files and MIME streams (emails). 
         [0048]    Email scanners  108  also include a plurality of decomposers  102 A-M. A decomposer is a component that can decompose items of a particular type to one ore more constituent items. A decomposition tree is a tree representing the current decomposition state of a compound item, with each node in the tree representing one item. An example of a decomposition tree  200  is shown in  FIG. 2 . The example of  FIG. 2  shows the decomposition of a compound item  202 , which is a MIME stream. Multipurpose Internet Mail Extensions (MIME) is an Internet Standard that extends the format of e-mail to support text in character sets other than US-ASCII, non-text attachments, multi-part message bodies, and header information in non-ASCII character sets. MIME is also a fundamental component of communication protocols such as HTTP, which requires that data be transmitted in the context of e-mail-like messages, even though the data may not actually be e-mail. 
         [0049]    MIME item  202  can be decomposed into a plurality of constituent items, such as MIME headers  204 , HyperText Markup Language (HTML) item  206 , and ZIP item  208 . Thus, decomposition tree  200  includes a number of branches. A decomposition sub-tree is a decomposition tree that is a branch of another decomposition tree. MIME headers  204  include information about MIME item  202  and about the items included in MIME item  202 , such as HTML item  206  and ZIP item  208 . Typically, a decomposer capable of decomposing MIME items will use MIME headers  204  to decompose MIME item  202  into its constituent items. HTML item  206  and ZIP item  208  are themselves compound items that may be decomposed into further constituent items. Thus, HTML item  206  and ZIP item  208  from decomposition sub-trees in  FIG. 2 . 
         [0050]    HTML item  206  includes information in the HTML language. HTML is a predominant markup language for the creation of web pages. It provides a means to describe the structure of text-based information in a document. HTML item  206  is a compound item that includes a plurality of items, such as text item  210 . HTML denotes certain text as headings, paragraphs, lists, and so on—and to supplement that text with interactive forms, embedded images, and other objects. Likewise, text item  210  includes a plurality of items, such as a list of Uniform Resource Locators (URLs)  212 . Each constituent item may be obtained by decomposing the inclusive item with one or more decomposers. 
         [0051]    ZIP item  208  includes information in the ZIP file format. The ZIP file format is a popular data compression and archival format. A ZIP file contains one or more files or documents, such as document  214 , which have been compressed or stored. Likewise, each document, such as document  214 , includes constituent items, such as text item  216 . Finally, text item  216  includes a plurality of items, such as a list of URLs  216 . Each constituent item may be obtained by decomposing the inclusive item with one or more decomposers. 
         [0052]    Each item in decomposition tree  200  may be scanned by a scanner that is the capable of scanning one or more different item types and scanning for one or more types of undesirable content. Compound items may, in some cases, be fully scanned by a scanner. However, typically, a compound item must be decomposed into its constituent items, and then each constituent item is scanned by the appropriate scanner. A scanner reports that it is satisfied by a decomposition tree when it has scanned the contents of that tree to its own satisfaction at the current state of decomposition. If all sub-trees of a decomposition tree satisfy a scanner than the decomposition tree satisfies that scanner. 
         [0053]    Exemplary psuedo-code samples of an exemplary method of scanner-driven decomposition are shown in  FIGS. 3-8 . This exemplary method is scanner-driven. This means the decomposition tree is only expanded as far as is necessary to satisfy all sub-trees for all scanners and no further. Thus unnecessary decompositions are avoided. One decomposition tree is used by all scanners so no decomposition step is carried out more than once. 
         [0054]    In the exemplary function  300 , shown in  FIG. 3 , each scanner is able to drive the decomposition to whatever level it requires to be satisfied by the sub-tree. The method is driven by a recursive function  300  that takes two parameters: a node in the decomposition tree and a list of scanners to scan with. In step  302 , each scanner in the list is called and returns whether or not it is satisfied. If a scanner is satisfied, it is removed from the list. For the first call (on the root node), the scanner list contains all of the available scanners. In step  304 , if there are any remaining scanners in the list, the current decomposition node is decomposed. In step  306 , the child nodes resulting from the decomposition performed in step  304  are scanned with the scanners remaining in the list. The root call completes when all scanners are satisfied by the whole decomposition tree. 
         [0055]    Each scanner implements a version of the function shown in  FIG. 4 . In the function  400 , shown in  FIG. 4 , each scanner is able to drive the decomposition to whatever level it requires to be satisfied by the sub-tree. In step  402 , function  400  determines whether the decomposition node being processed is a type that is supported by the scanner. In step  404 , if the node is supported, the node is scanned, including recursively further decomposing the node. 
         [0056]    Each node in the decomposition tree supports the functions shown in  FIGS. 5 and 6 . The function  500 , shown in  FIG. 5 , attempts to decompose one more level in the sub-tree to the specified type by, in step  502 , invoking each decomposer in turn. The function  600  shown in  FIG. 6  attempts to establish the type of the node by, in step  602 , invoking each decomposer in turn. 
         [0057]    Each decomposer supports the functions shown in  FIGS. 7 and 8 . In the function  700 , shown in  FIG. 7 , the decomposer, in step  702 , establishes whether the given item is of a type it recognizes. In the function  800 , shown in  FIG. 8 , the decomposer carries out its decomposition, first, in step  802 , determining whether it supports either node, then, in step  804 , creating additional nodes in the decomposition tree as required. 
         [0058]    Examples of scanners that may be used, and their characteristics, are shown in  FIG. 9 . For example, scanner  902  may be an anti-virus scanner, an anti-spam scanner, a bad content scanner, etc. Each scanner has associated item types that may be satisfied by a scan  904 , such as documents, HTML items, MIME items, text items, etc. Likewise, each scanner has associated item types that it can scan  906 , such as MIME items, documents, HTML items, MIME headers, text items, lists of URLs, etc. 
         [0059]    It is to be noted that the scanners shown in  FIG. 9  are merely examples. The present invention contemplates use with any type of scanner, and scanners capable of scanning any type of item. 
         [0060]    Examples of decomposers that may be used, and their characteristics, are shown in  FIG. 10 . For example, decomposer  1002  may decompose MIME items, ZIP items, HTML items, text items, documents, etc. Each decomposer has associated item types that may be decomposed from  1004 , such as MIME items, ZIP items, HTML items, text items, documents, etc. Likewise, each scanner has decomposer item types that it can decompose items to  1004 , such as MIME headers, HTML items, unknown items, text items, lists of URLs, etc. 
         [0061]    It is to be noted that the decomposers shown in  FIG. 10  are merely examples. The present invention contemplates use with any type of decomposer, and decomposer capable of decomposing any type of item. 
         [0062]    An example of processing of a data stream using scanner-driven decomposition is shown in  FIGS. 11-16 . This example assumes that the data stream contains no viruses, spam or bad content. The example is best viewed in conjunction with the decomposition tree  200 , shown in  FIG. 2 . At the first stage of the decomposition example, the decomposition tree includes only MIME item  202 , as shown in  FIG. 11   a . Turning to  FIG. 11   b , it is seen that the unsatisfied scanners at the beginning of this stage  1102  include the anti-virus scanner, the anti-spam scanner and the bad content scanner. The actions taken by each scanner at this stage  1104  are that the anti-virus scanner recognizes the item as MIME and scans it, the anti-spam scanner recognizes the item as MIME and begins to scan by performing a top level decomposition, and the bad content scanner is not run as it cannot handle MIME items. The result of this stage  1106  is that all scanners are unsatisfied. 
         [0063]    At the second stage of the decomposition example, the decomposition tree includes MIME item  202 , MIME headers  204  and HTML item  206 , as shown in  FIG. 12   a . Turning to  FIG. 12   b , it is seen that the unsatisfied scanners at the beginning of this stage  1202  include the anti-virus scanner, the anti-spam scanner and the bad content scanner. The actions taken by each scanner at this stage  1204  are the anti-spam scanner decomposes the MIME headers node  202  and scans it. As is cannot determine whether the mail is spam on this basis alone it decomposes to the HTML node  206  and scans that. The bad content scanner is not run as it cannot handle MIME items and the anti-virus scanner is also not run. The result of this stage  1206  is that all scanners are unsatisfied. 
         [0064]    At the third stage of the decomposition example, the decomposition tree includes MIME item  202 , MIME headers  204 , HTML item  206 , text item  210  and list of URLs  212 , as shown in  FIG. 13   a . Turning to  FIG. 13   b , it is seen that the unsatisfied scanners at the beginning of this stage  1302  include the anti-virus scanner, the anti-spam scanner and the bad content scanner. The actions taken by each scanner at this stage  1304  are the anti-spam scanner is still not able to complete and so decomposes and scans body text and URLs. It has now established that the MIME message is not spam and so is satisfied by the whole decomposition tree. The bad content scanner and the anti-virus scanner are not run. The result of this stage  1306  is that the anti-spam scanner is satisfied and the bad content scanner and the anti-virus scanner are unsatisfied. 
         [0065]    At the fourth stage of the decomposition example, the decomposition tree includes MIME item  202 , MIME headers  204 , HTML item  206 , text item  210  and list of URLs  212 , as shown in  FIG. 14   a . Turning to  FIG. 14   b , it is seen that the unsatisfied scanners at the beginning of this stage  1402  include the anti-virus scanner and the bad content scanner. The actions taken by each scanner at this stage  1404  are the anti-virus scanner scans the MIME headers item and, as it is not interested in that type, reports that it is not satisfied by it. The bad content scanner scans the MIME headers item and reports that it is satisfied by it. The anti-virus scanner scans the HTML and reports that it is satisfied by it. The bad content scanner reports that is not satisfied by HTML. It is then presented with the Text node, which it scans, and reports that it is satisfied by. Note that this entire step does not involve any new decompositions. The result of this stage  1406  is that the bad content scanner is satisfied and the anti-virus scanner is not satisfied. 
         [0066]    At the fifth stage of the decomposition example, the decomposition tree includes MIME item  202 , MIME headers  204 , HTML item  206 , text item  210 , list of URLs  212 , ZIP item  208  and document  214 , as shown in  FIG. 15   a . Turning to  FIG. 15   b , it is seen that the unsatisfied scanners at the beginning of this stage  1502  include the anti-virus scanner and the bad content scanner (which is not satisfied now that additional decomposition has occurred). The actions taken by each scanner at this stage  1504  are the anti-virus scanner decomposes the ZIP item  208  and scans the document  214  and is satisfied by it. The bad content scanner does not handle these types of items and so is not satisfied. The result of this stage  1506  is that the bad content scanner is not satisfied and the anti-virus scanner is satisfied. 
         [0067]    At the sixth stage of the decomposition example, the decomposition tree includes MIME item  202 , MIME headers  204 , HTML item  206 , text item  210 , list of URLs  212 , ZIP item  208 , document  214 , and text item  216 , as shown in  FIG. 16   a . Turning to  FIG. 16   b , it is seen that the unsatisfied scanners at the beginning of this stage  1602  include only the bad content scanner. The actions taken by each scanner at this stage  1404  are that the bad content scanner decomposes document  214  to text item  216 , scans it and is satisfied. All scanners are now satisfied for all subtrees of MIME and therefore the scan is complete. The result of this stage  1606  is that all scanners are satisfied. 
         [0068]    The example shown in  FIGS. 11-16  shows how the method can scan a decomposition tree using three scanners without performing any decomposition steps more than once. However, virtually the entire decomposition tree is expanded (only the final URL list step is avoided). In the example shown in  FIGS. 17-20 , it is assumed that the MIME message is a spam than can be detected as such purely on the basis of its headers. Stage  1  is as shown in  FIG. 11 . From there the scan proceeds with stage two, shown in  FIGS. 17   a  and  17   b . At the second stage of this example, the decomposition tree includes MIME item  202  and MIME headers  204 , as shown in  FIG. 17   a . All scanners are initially unsatisfied  1702 , as shown in  FIG. 17   b . The actions taken  1704  are that the anti-spam scanner decomposes the MIME Headers and scans them. On this basis it is able to determining that the mail is spam and completes its scan without any further decomposition. The anti-virus scanner and the bad content scanner are not run. The result  1706  is that the anti-spam scanner is satisfied by the MIME items, and the anti-virus and bad content scanners are not satisfied. 
         [0069]    At the third stage of this example, the decomposition tree includes MIME item  202  and MIME headers  204 , as shown in  FIG. 18   a . Turning to  FIG. 18   b , it is seen that the unsatisfied scanners  1802  include the anti-virus scanner and the bad content scanner. The actions taken  1804  are that the anti-virus scanner scans the MIME headers item and as it is not interested in that type reports that it is satisfied by it. The bad content scanner scans the MIME headers item and reports that it is satisfied by it. The result  1806  is that the anti-virus scanner is satisfied by the MIME items, and the bad content scanner is not satisfied. 
         [0070]    At the fourth stage of this example, the decomposition tree includes MIME item  202 , MIME headers  204 , and HTML item  206 , as shown in  FIG. 19   a . Turning to  FIG. 19   b , it is seen that the unsatisfied scanners  1902  include the anti-virus scanner (which has not examined the HTML item  206 ) and the bad content scanner. The actions taken  1904  are that as the MIME items have not satisfied all scanners the HTML node  206  is decomposed. The anti-virus scanner scans HTML item  206  and is satisfied by it. The bad content scanner is not satisfied however. The result  1906  is that the anti-virus scanner is satisfied by HTML item  206 , and the bad content scanner is not satisfied. 
         [0071]    At the fifth stage of this example, the decomposition tree includes MIME item  202 , MIME headers  204 , HTML item  206 , and text item  210 , as shown in  FIG. 20   a . Turning to  FIG. 20   b , it is seen that the unsatisfied scanners  2002  include the bad content scanner. The actions taken  2004  are that the bad content scanner scans text item  210  and is satisfied. The result  2006  is that the bad content scanner is satisfied by text item  210 . 
         [0072]    The sixth stage of this example is similar to that shown in  FIG. 16 , although the method recursively decomposed the ZIP item  208  because at a previous stage, at which the recursion occurs, scanners were unsatisfied. At completion, the decomposition tree includes MIME item  202 , MIME headers  204 , HTML item  206 , text item  210 , ZIP item  208 , document  214 , and text item  218 , as shown in  FIG. 21 . Thus, it is seen that at completion one more decomposition step has been avoided. 
         [0073]    In another example, the method can scan a decomposition tree using two scanners (not using the bad content scanner). In this example, there is no need to decompose the HTML node or the Document node and the final decomposition tree includes MIME item  202 , MIME headers  204 , HTML item  206 , ZIP item  208 , and document  214 . Two more decomposition steps have been avoided. 
         [0074]    The described method is one possible way of implementing a scanner-driven model that is both simple and modular, allowing the addition of zero or more decomposers and scanners as are required by particular products in particular situations. A number of implementations of the method are possible. The present invention contemplates and and all such implementations. 
         [0075]    An exemplary block diagram of an email server  2300 , in which the present invention may be implemented, is shown in  FIG. 23 . Email server  2300  is typically a programmed general-purpose computer system, such as a personal computer, workstation, server system, and minicomputer or mainframe computer. Email server  2300  includes one or more processors (CPUs)  2302 A- 2302 N, input/output circuitry  2304 , network adapter  2306 , and memory  2308 . CPUs  2302 A- 2302 N execute program instructions in order to carry out the functions of the present invention. Typically, CPUs  2302 A- 2302 N are one or more microprocessors, such as an INTEL PENTIUM® processor.  FIG. 23  illustrates an embodiment in which email server  2300  is implemented as a single multi-processor computer system, in which multiple processors  2302 A- 2302 N share system resources, such as memory  2308 , input/output circuitry  2304 , and network adapter  2306 . However, the present invention also contemplates embodiments in which email server  2300  is implemented as a plurality of networked computer systems, which may be single-processor computer systems, multi-processor computer systems, or a mix thereof. 
         [0076]    Input/output circuitry  2304  provides the capability to input data to, or output data from, email server  2300 . For example, input/output circuitry may include input devices, such as keyboards, mice, touchpads, trackballs, scanners, etc., output devices, such as video adapters, monitors, printers, etc., and input/output devices, such as, modems, etc. Network adapter  2306  interfaces email server  2300  with Internet/intranet  2310 . Internet/intranet  2310  may include one or more standard local area network (LAN) or wide area network (WAN), such as Ethernet, Token Ring, the Internet, or a private or proprietary LANIWAN. 
         [0077]    Memory  2308  stores program instructions that are executed by, and data that are used and processed by, CPU  2302  to perform the functions of email server  2300 . Memory  2308  may include electronic memory devices, such as random-access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), electrically erasable programmable read-only memory (EEPROM), flash memory, etc., and electro-mechanical memory, such as magnetic disk drives, tape drives, optical disk drives, etc., which may use an integrated drive electronics (IDE) interface, or a variation or enhancement thereof, such as enhanced IDE (EIDE) or ultra direct memory access (UDMA), or a small computer system interface (SCSI) based interface, or a variation or enhancement thereof, such as fast-SCSI, wide-SCSI, fast and wide-SCSI, etc, or a fiber channel-arbitrated loop (FC-AL) interface. 
         [0078]    In the example shown in  FIG. 23 , memory  2308  includes email processing software  2312  and operating system  2314 . Email processing software  2312  includes email scanners  208 , which include scanners  118 A-N, decomposers  120 A-M, and scanner-driven decomposition routines  212 , quarantined emails  210 , spam emails  212 , clean emails  214 , recipient inboxes  216 , and, as well as additional functionality that is not shown. Email scanners  208  automate the highlighting, removal or filtering of e-mail spam by scanning through incoming and outgoing e-mails in search of traits typical of spam. Such scanning may include searching for patterns in the headers or bodies of messages. Each incoming email message is scanned to determine whether it is a spam email message that is to be marked as SPAM, a dangerous spam email message that is to be quarantined, or a clean email message that is to be delivered as is to the recipient&#39;s inbox. In addition, email scanner  208  scans the email address of the sender of the email, and may also scan the first and last name of the sender of the email. Scanners  118 A-N and decomposers  120 A-M decompose the email messages into their constituent items and scan the items to determine their status. Each incoming email message is scanned to determine whether it is a dangerous spam email message that is to be quarantined  110 , a spam email message that is to be marked as SPAM  112  and delivered to the recipients inbox  114 , or a clean email message  116  that is to be delivered as is to the recipient&#39;s inbox  114 . Scanner-driven decomposition routines control the operation of scanners  118 A-N and decomposers  120 A-M to scan the email messages using the scanner-driven method described above. Operating system  2114  provides overall system functionality. 
         [0079]    As shown in  FIG. 23 , the present invention contemplates implementation on a system or systems that provide multi-processor, multi-tasking, multi-process, and/or multi-thread computing, as well as implementation on systems that provide only single processor, single thread computing. Multi-processor computing involves performing computing using more than one processor. Multi-tasking computing involves performing computing using more than one operating system task. A task is an operating system concept that refers to the combination of a program being executed and bookkeeping information used by the operating system. Whenever a program is executed, the operating system creates a new task for it. The task is like an envelope for the program in that it identifies the program with a task number and attaches other bookkeeping information to it. Many operating systems, including UNIX®, OS/2®, and Windows®, are capable of running many tasks at the same time and are called multitasking operating systems. Multi-tasking is the ability of an operating system to execute more than one executable at the same time. Each executable is running in its own address space, meaning that the executables have no way to share any of their memory. This has advantages, because it is impossible for any program to damage the execution of any of the other programs running on the system. However, the programs have no way to exchange any information except through the operating system (or by reading files stored on the file system). Multi-process computing is similar to multi-tasking computing, as the terms task and process are often used interchangeably, although some operating systems make a distinction between the two. 
         [0080]    It is important to note that while the present invention has been described in the context of a fully functioning data processing system, those of ordinary skill in the art will appreciate that the processes of the present invention are capable of being distributed in the form of a computer readable medium of instructions and a variety of forms and that the present invention applies equally regardless of the particular type of signal bearing media actually used to carry out the distribution. Examples of computer readable media include recordable-type media such as floppy disc, a hard disk drive, RAM, and CD-ROM&#39;s, as well as transmission-type media, such as digital and analog communications links. 
         [0081]    Although specific embodiments of the present invention have been described, it will be understood by those of skill in the art that there are other embodiments that are equivalent to the described embodiments. For example, the present invention may be advantageously employed in scanning outgoing email messages, as well as incoming email messages. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrated embodiments, but only by the scope of the appended claims.