Method and apparatus for filtering electronic messages

Abstract

A method is provided for filtering electronic messages such as unsolicited bulk email. The method includes establishing a communications connection with the remote server under the Simple Email Transfer Protocol or other suitable protocol; accepting session data from the remote server; and determining if the session data meets criteria associated with legitimate messages. If the data pertaining to the connection does not meet the criteria associated with legitimate messages, then one or more stimulus signals are sent to the remote server. If the server responds to the stimulus signal in the manner required by the communications protocol, then the session can be added to a database of known sessions. The session is then terminated by responding to the server with a temporary error message in accordance with the protocol. If the remote server is a legitimate server complying with the STMP, it will resend the message after a prescribed time period.

1 . A method for processing an email message having message content and sent by a remote server in accordance with a communications protocol, the method comprising:
 establishing a communications connection with the remote server;   exchanging a plurality of session messages defining a communications session with the remote server, at least some of which are separate from the message content;   accepting from the remote server session data pertaining to the communications connection, including information pertaining to at least one of the following: the remote server, the sender of the email message, and the destination of the email message;   testing the behavior of the remote server to generate a machine-originated response from the remote server in accordance with the communications protocol to determine if the remote server is operating in accordance with the communications protocol, the testing initiated during the communications session; and   processing the communications connection in response to whether the remote server is operating in accordance with the communications protocol.   
   
   
       2 . The method of  claim 1 , wherein testing the behavior includes sending at least one stimulus signal to the remote server. 
   
   
       3 . The method of  claim 2 , wherein the step of processing the communications connection includes accepting the message content if the remote server responds to the stimulus signal in the manner required by the communications protocol. 
   
   
       4 . The method of  claim 2 , wherein the at least one stimulus signal is one of a command and a reply, the format and content of which are specified by the communications protocol. 
   
   
       5 . The method of  claim 2 , wherein the at least one stimulus signal does not comply with the protocol in terms of at least one of timing, format and content. 
   
   
       6 . The method of  claim 1 , further comprising, exchanging a plurality of session messages defining the communications session, at least some of which are separate from the message content. 
   
   
       7 . The method of  claim 6 , wherein testing the behavior includes waiting a predetermined amount of time after receiving at least one of the plurality of session messages from the remote server before sending a stimulus signal to the remote server. 
   
   
       8 . The method of  claim 6 , wherein testing the behavior includes terminating the communications session when at least one of the plurality of session messages from the remote server are transmitted in the wrong order. 
   
   
       9 . The method of  claim 1 , wherein the communications protocol is the Simple Mail Transport Protocol. 
   
   
       10 . The method of  claim 1 , wherein testing the behavior includes terminating the communications connection. 
   
   
       11 . The method of  claim 1 , wherein processing the communications connection includes accepting the message content when the remote server behaves in the manner required by the communications protocol. 
   
   
       12 . The method of  claim 1 , wherein testing the behavior of the remote server comprises:
 sending to the remote server at least one session message, the format and content of which are specified by the communications protocol, wherein the session message is configured to generate a machine-originated response from the remote server in accordance with the communications protocol; and   determining whether the remote server responds to the session message in accordance with the communications protocol.   
   
   
       13 . An apparatus for processing an email message having message content and sent by a remote server in accordance with a communications protocol, comprising:
 a communications port adapted for establishing a communications connection with the remote server;   a processor coupled to the communications port and adapted to:
 establish a communications connection with the remote server; 
 exchange a plurality of session messages defining a communications session with the remote server, at least some of which are separate from the message content; 
 accept from the remote server session data pertaining to the communications connection, including information pertaining to at least one of the following: the remote server, the sender of the email message, and the destination of the email message; 
 test the behavior of the remote server to generate a machine-originated response from the remote server in accordance with the communications protocol to determine if the remote server is operating in accordance with the communications protocol, the testing initiated during the communications session; and 
 process the communications connection in response to whether the remote server is operating in accordance with the communications protocol. 
   
   
   
       14 . The apparatus of  claim 13 , wherein the communications protocol is the Simple Mail Transport Protocol. 
   
   
       15 . The apparatus of  claim 13 , wherein testing the behavior includes sending at least one stimulus signal to the remote server. 
   
   
       16 . The apparatus of  claim 15 , wherein processing the communications connection includes accepting the message content if the remote server responds to the stimulus signal in the manner required by the communications protocol. 
   
   
       17 . The apparatus of  claim 15 , wherein the at least one stimulus signal is one of a command and a reply, the format and content of which are specified by the communications protocol. 
   
   
       18 . The apparatus of  claim 13 , wherein testing the behavior includes terminating the communications connection. 
   
   
       19 . The apparatus of  claim 13 , wherein testing the behavior of the remote server comprises:
 sending to the remote server at least one session message, the format and content of which are specified by the communications protocol, wherein the session message is configured to generate a machine-originated response from the remote server in accordance with the communications protocol; and   determining whether the remote server responds to the session message in accordance with the communications protocol.   
   
   
       20 . A communications system for processing an email message, comprising:
 a communications network;   a remote server connected to the communications network and adapted to send the email message in accordance with a communications protocol; and   a receiving server connected to the communications network and adapted to exchange a plurality of session messages containing session data and defining a communications session with the remote server, the receiving server comprising:
 a connection assessment module adapted to assess the session data; and 
 a connection behavior testing module adapted to test the behavior of the remote server during the communications session to generate a machine-originated response from the remote server in accordance with the communications protocol to determine if the remote server is operating in accordance with the communications protocol.