Method and system for blocking e-mail having a nonexistent sender address

• US 7,249,175 B1
• Filed: 04/12/2000
• Issued: 07/24/2007
• Est. Priority Date: 11/23/1999
• Status: Expired due to Fees

• Current Assignee: Escom Corporation
• Original Assignee: Escom Corporation
• Inventors: Donaldson, Albert L.
• Primary Examiner(s): Winder, Patrice L.
• Application Number:
  US09/548,322
• Time in Patent Office: 2,659 Days
• Field of Search: 709/206, 709/207, 709/204, 709/229, 713/200, 713/201
• US Class Current: 709/225
• CPC Class Codes: G06Q 10/107 Computer-aided management of electronic mailing [e-mailing]
• CPC Class Codes: H04L 51/212 using filtering or selective blocking
• CPC Class Codes: H04L 63/0236 Filtering by address, protocol, port number or service, e.g. IP-address or URL

Abstract

A system and method for filtering undesirable e-mail with forged nonexistent sender addresses in real time without sending a message to that sender. A server or proxy rejects electronic messages having a nonexistent sender address by establishing a connection to an authorized mailhost for the domain of the sender address and using discrete transactions during the protocol setup phase to determine if that mailhost will accept mail for the sender address. If the authorized mailhost for the sender address will not accept mail for that address, then the sender address is determined to not exist and the message can be safely rejected.

Claims

1. A method for selectively accepting an electronic message having a sender address, the method comprising establishing a test connection to an authorized server for the sender address in accordance with Simple Mail Transfer Protocol (SMTP), sending a SMTP RCPT command specifying the sender address to the authorized server, and rejecting the electronic message if the authorized server does not affirmatively accept the SMTP RCPT command.

2. The method of claim 1, further comprising accepting the electronic message if the authorized server affirmatively accepts the SMTP RCPT command.

3. The method of claim 2, further comprising sending a SMTP DATA command to the authorized server and rejecting the electronic message if the authorized server does not affirmatively accept the SMTP DATA command.

4. The method of claim 2, further comprising sending message data to the authorized server, and rejecting the electronic message if the authorized server does not affirmatively accept the message data.

5. The method of claim 1, wherein the authorized server is a mail exchanger host for the domain of the e-mail address.

6. The method of claim 1, wherein the authorized server has the same name as the domain of the sender address.

7. The method of claim 1, further comprising sending a SMTP MAIL command to the authorized server, the SMTP MAIL command specifying a complete e-mail address.

8. The method of claim 1, further comprising sending a SMTP MAIL command to the authorized server, the SMTP MAIL command specifying the null address “

<

>

”

.

9. A system for selectively accepting an electronic message having a sender address, the system comprising a filter establishing a test connection to an authorized server for the sender address in accordance with Simple Mail Transfer Protocol (SMTP), sending a SMTP RCPT command specifying the sender address to the authorized server, and rejecting the electronic message if the authorized server does not affirmatively accept the SMTP RCPT command.

10. The system of claim 9, further comprising accepting the electronic message if the authorized server affirmatively accepts the SMTP RCPT command.

11. The system of claim 10, further comprising sending a SMTP DATA command to the authorized server and rejecting the electronic message if the authorized server does not affirmatively accept the SMTP DATA command.

12. The system of claim 10, further comprising sending message data to the authorized server, and rejecting the electronic message if the authorized server does not affirmatively accept the message data.

13. The system of claim 9, wherein the authorized server is a mail exchanger host for the domain of the e-mail address.

14. The system of claim 9, wherein the authorized server has the same name as the domain of the sender address.

15. The system of claim 9, further comprising sending a SMTP MAIL command to the authorized server, the SMTP MAIL command specifying a complete e-mail address.

16. The system of claim 9, further comprising sending a SMTP MAIL command to the authorized server, the SMTP MAIL command specifying the null address “

<

>

”

.

17. An article of manufacture for selectively accepting an electronic message having a sender address, the article of manufacture comprising a computer-readable medium having stored thereon instructions which, when performed by a processor, cause the processor to execute the steps comprising the steps of:

establishing a test connection to an authorized server for the sender address in accordance with Simple Mail Transfer Protocol (SMTP), sending a SMTP RCPT command specifying the sender address to the authorized server, and rejecting the electronic message if the authorized server does not affirmatively accept the SMTP RCPT command.

18. The article of manufacture of claim 17, further comprising accepting the electronic message if the authorized server affirmatively accepts the SMTP RCPT command.

19. The article of claim 18, further comprising sending a SMTP DATA command to the authorized server and rejecting the electronic message if the authorized server does not affirmatively accept the SMTP DATA command.

20. The article of claim 18, further comprising sending message data to the authorized server, and rejecting the electronic message if the authorized server does not affirmatively accept the message data.

21. The article of manufacture of claim 17, wherein the authorized server is a mail exchanger host for the domain of the e-mail address.

22. The article of manufacture of claim 17, wherein the authorized server has the same name as the domain of the sender address.

23. The article of claim 17, further comprising sending a SMTP MAIL command to the authorized server, the SMTP MAIL command specifying a complete e-mail address.

24. The article of claim 17, further comprising sending a SMTP MAIL command to the authorized server, the SMTP MAIL command specifying the null address “

<

>

”

.

25. A method for selectively accepting an electronic message having a sender address, the method comprising establishing a test connection to an authorized server for the sender address, sending to the authorized server a recipient command as defined by a protocol to identify an individual electronic message recipient, the recipient command specifying the sender address as the individual recipient, and rejecting the electronic message if the authorized server does not affirmatively accept the recipient command.

26. The method of claim 25, further comprising accepting the electronic message if the authorized server affirmatively accepts the recipient command.

27. The method of claim 26, wherein the recipient command does not use any command provided explicitly for the purpose of verifying a user address, such as the Simple Mail Transfer Protocol (SMTP) VRFY command.

28. A system for selectively accepting an electronic message having a sender address, the system comprising a filter establishing a test connection to an authorized server for the sender address, sending to the authorized server a recipient command as defined by a protocol to identify an individual electronic message recipient, the recipient command specifying the sender address as the individual recipient, and rejecting the electronic message if the authorized server does not affirmatively accept the recipient command.

29. The system of claim 28, further comprising accepting the electronic message if the authorized server affirmatively accepts the recipient command.

30. The system of claim 28, wherein the recipient command does not use any command provided explicitly for the purpose of verifying a user address, such as the Simple Mail Transfer Protocol (SMTP) VRFY command.

31. An article of manufacture for selectively accepting an electronic message having a sender address, the article of manufacture comprising a computer-readable medium having stored thereon instructions which, when performed by a processor, cause the processor to execute the steps comprising the steps of:

establishing a test connection to an authorized server for the sender address, sending to the authorized server a recipient command as defined by a protocol to identify an individual electronic message recipient, the recipient command specifying the sender address as the individual recipient, and rejecting the electronic message if the authorized server does not affirmatively accept the recipient command.

32. The article of manufacture of claim 31, further comprising accepting the electronic message if the authorized server affirmatively accepts the recipient command.

33. The article of manufacture of claim 31, wherein the recipient command does not use any command provided explicitly for the purpose of verifying a user address, such as the Simple Mail Transfer Protocol (SMTP) VRFY command.