07249175 is referenced by 273 patents and cites 37 patents.

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.

Title
Method and system for blocking e-mail having a nonexistent sender address
Application Number
9/548322
Publication Number
7249175 (B1)
Application Date
April 12, 2000
Publication Date
July 24, 2007
Inventor
Albert L Donaldson
Oakton
VA, US
Agent
Blank Rome
Assignee
Escom Corporation
VA, US
IPC
G06F 15/173
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