System and Method for Detecting Unwanted Content

1. A method comprising: receiving, at a server from a first user, an electronic message having one or more addressees; comparing a representation of the electronic message to representations of one or more electronic messages previously sent by the first user during a predetermined time period; if the electronic message was previously sent by the first user during the predetermined time period, incrementing a message count associated with the electronic message; if the electronic message was not previously sent by the first user during the predetermined time period, storing the representation of the electronic message; updating a message uniqueness metric in a manner depending on whether the electronic message had been sent previously during the predetermined time period; wherein the message uniqueness metric reflects a percentage of electronic messages sent by the first user during the predetermined time period that were unique; comparing the updated message uniqueness metric to a threshold message uniqueness value indicative of distribution of unwanted content; determining, based on the comparing of the updated message uniqueness metric, whether the electronic message contains unwanted content; delivering the electronic message if the updated message uniqueness metric indicates that the electronic message does not contain unwanted content; and refraining from delivering the electronic message if the updated message uniqueness metric indicates that the electronic message contains unwanted content.

2. The method of claim 1 , further comprising: for each addressee in the one or more addressees, updating a peer symmetry metric to reflect whether the first user is included in an address book of the addressee; updating a message rate reflecting a rate at which the first user is sending electronic messages; and comparing the updated message rate to one or more threshold message rates.

3. The method of claim 2 , further comprising: adding the first user to an address book of a second user; and updating the peer symmetry metric.

4. The method of claim 2 , further comprising: if the updated message rate exceeds a first message rate threshold, preventing the user from sending additional electronic messages; and if the updated message rate exceeds a second message rate threshold, but not the first message rate threshold, add the first user to a watch list.

5. The method of claim 4 , further comprising, if the user is placed in the watch list: initiating tracking of a peer uniqueness metric identifying a percentage of addressees of electronic messages sent by the first user that are unique.

6. The method of claim 5 , wherein tracking the peer uniqueness metric comprises: comparing a first addressee of the electronic message to addressees of one or more previous electronic messages sent by the first user during a predetermined time period; if the first addressee was previously sent an electronic message from the first user during the predetermined time period, incrementing a message count associated with the first addressee; if the first addressee was not previously sent an electronic message from the first user during the predetermined time period, recording the first addressee; and updating the peer uniqueness metric depending on whether the first addressee previously had been sent a message by the first user during the predetermined time period.

7. The method of claim 1 , further comprising: receiving from a second user a block request regarding the first user; incrementing a total block count of the first user; updating a block rate reflecting a rate at which the first user is blocked by other users; and adding the first user to the watch list if the block rate exceeds a first block rate threshold.

8. The method of claim 1 , further comprising, prior to said receiving from the first user an electronic message: logging the first user into a computer system hosting an application for sending electronic messages; retrieving from storage a first set of metrics, including a total block count reflecting how many other users have blocked the first user; if the user is included in a watch list, retrieving from storage a second set of metrics, including: the message uniqueness metric; and a peer uniqueness metric identifying a percentage of addressees of electronic messages sent by the first user that are unique; and if the user is not identified on the watch list, initializing the second set of metrics.

9. The method of claim 8 , further comprising: retrieving a first list of other users to whom the first user is subscribed; retrieving a second list of other users that have blocked the first user; and striking from the first list any users identified in the second list.

10. The method of claim 1 , further comprising: logging the user out of a computer system hosting an application for sending electronic messages; storing a first set of metrics, including a total block count reflecting how many other users have blocked the first user; and if the user is included in a watch list, storing a second set of metrics, including: the message uniqueness metric; and a peer uniqueness metric identifying a percentage of addressees of electronic messages sent by the first user that are unique.

11. A non-transitory computer-readable medium storing instructions that, when executed by a processor, cause the processor to perform a method comprising: receiving, at a server from a first user, an electronic message having one or more addressees; comparing a representation of the electronic message to representations of one or more electronic messages previously sent by the first user during a predetermined time period; if the electronic message was previously sent by the first user during the predetermined time period, incrementing a message count associated with the electronic message; if the electronic message was not previously sent by the first user during the predetermined time period, storing the representation of the electronic message; updating a message uniqueness metric in a manner depending on whether the electronic message had been sent previously during the predetermined time period; wherein the message uniqueness metric reflects a percentage of electronic messages sent by the first user during the predetermined time period that were unique; comparing the updated message uniqueness metric to a threshold message uniqueness value indicative of distribution of unwanted content; determining, based on the comparing of the updated message uniqueness metric, whether the electronic message contains unwanted content; delivering the electronic message if the updated message uniqueness metric indicates that the electronic message does not contain unwanted content; and refraining from delivering the electronic message if the peer symmetry metric or the comparison indicates that the electronic message contains unwanted content.

12. An apparatus comprising: one or more processors; and a non-transitory computer-readable medium storing instructions that, when executed by the one or more processors, cause the apparatus to: receive, at a server from a first user, an electronic message having one or more addressees; compare a representation of the electronic message to representations of one or more electronic messages previously sent by the first user during a predetermined time period; if the electronic message was previously sent by the first user during the predetermined time period, increment a message count associated with the electronic message; if the electronic message was not previously sent by the first user during the predetermined time period, store the representation of the electronic message; update a message uniqueness metric in a manner depending on whether the electronic message had been sent previously during the predetermined time period; compare the updated message uniqueness metric to a threshold message uniqueness value indicative of distribution of unwanted content; determine, based on the comparing of the updated message uniqueness metric, whether the electronic message contains unwanted content; deliver the electronic message if the updated message uniqueness metric indicates that the electronic message does not contain unwanted content; and refrain from delivering the electronic message if the updated message uniqueness metric indicates that the electronic message contains unwanted content.

13. The apparatus of claim 12 , the non-transitory computer-readable storage medium further storing instructions that, when executed by the one or more processors, cause the apparatus to: for each addressee in the one or more addressees, update a peer symmetry metric to reflect whether the first user is included in an address book of the addressee; update a message rate reflecting a rate at which the first user is sending electronic messages; and compare the updated message rate to one or more threshold message rates.

14. The apparatus of claim 13 , the non-transitory computer-readable storage medium further storing instructions that, when executed by the one or more processors, cause the apparatus to: add the first user to an address book of a second user; and update the peer symmetry metric.

15. The apparatus of claim 13 , the non-transitory computer-readable storage medium further storing instructions that, when executed by the one or more processors, cause the apparatus to: if the updated message rate exceeds a first message rate threshold, prevent the user from sending additional electronic messages; and if the updated message rate exceeds a second message rate threshold, but not the first message rate threshold, add the first user to a watch list.

16. The apparatus of claim 15 , the non-transitory computer-readable storage medium further storing instructions that, when executed by the one or more processors, cause the apparatus to: if the user is placed in the watch list, initiate tracking of a peer uniqueness metric identifying a percentage of addressees of electronic messages sent by the first user that are unique.

17. The apparatus of claim 16 , wherein tracking the peer uniqueness metric comprises: comparing a first addressee of the electronic message to addressees of one or more previous electronic messages sent by the first user during a predetermined time period; if the first addressee was previously sent an electronic message from the first user during the predetermined time period, incrementing a message count associated with the first addressee; if the first addressee was not previously sent an electronic message from the first user during the predetermined time period, recording the first addressee; and updating the peer uniqueness metric depending on whether the first addressee previously had been sent a message by the first user during the predetermined time period.

18. The apparatus of claim 12 , the non-transitory computer-readable storage medium further storing instructions that, when executed by the one or more processors, cause the apparatus to: receive from a second user a block request regarding the first user; increment a total block count of the first user; update a block rate reflecting a rate at which the first user is blocked by other users; and add the first user to the watch list if the block rate exceeds a first block rate threshold.

19. The apparatus of claim 12 , the non-transitory computer-readable storage medium further storing instructions that, when executed by the one or more processors, cause the apparatus to, prior to said receiving from the first user an electronic message: log the first user into a computer system hosting an application for sending electronic messages; retrieve from storage a first set of metrics, including a total block count reflecting how many other users have blocked the first user; if the user is included in a watch list, retrieve from storage a second set of metrics, including: the message uniqueness metric; and a peer uniqueness metric identifying a percentage of addressees of electronic messages sent by the first user that are unique; and if the user is not identified on the watch list, initialize the second set of metrics.

20. The apparatus of claim 19 , the non-transitory computer-readable storage medium further storing instructions that, when executed by the one or more processors, cause the apparatus to: retrieve a first list of other users to whom the first user is subscribed; retrieve a second list of other users that have blocked the first user; and strike from the first list any users identified in the second list.

21. The apparatus of claim 12 , the non-transitory computer-readable storage medium further storing instructions that, when executed by the one or more processors, cause the apparatus to: log the user out of a computer system hosting an application for sending electronic messages; store a first set of metrics, including a total block count reflecting how many other users have blocked the first user; and if the user is included in a watch list, store a second set of metrics, including: the message uniqueness metric; and a peer uniqueness metric identifying a percentage of addressees of electronic messages sent by the first user that are unique.