SMTP network security processing in a transparent relay in a computer network

A method of processing e-mail communications for network security, the method comprising:

• transparently receiving in a computer configured as an SMTP transparent relay diverted e-mail packets originated by an SMTP e-mail client to be sent to an e-mail server, the e-mail server being configured as a mail transfer agent, each of the diverted e-mail packets having a destination IP address that does not correspond to any of the computer as received for processing by the computer, the SMTP transparent relay including a communication interface for each of the e-mail server and the SMTP client running in promiscuous mode;
• in the computer, checking the diverted e-mail packets originated by the SMTP e-mail client for connection initiation packets configured to initiate an e-mail connection between the SMTP e-mail client and the e-mail server;
• determining whether the connection initiation packets violate a first policy in a plurality of network security policies;
• and
• performing a first policy action on the connection initiation packets if the connection initiation packets violate the first policy.

A method of processing computer communications for network security, the method comprising:

• transparently receiving in a computer configured as an SMTP transparent relay diverted packets between a client computer configured as an SMTP e-mail client and a server computer configured as a mail transfer agent communicating over a communication session in accordance with SMTP, the diverted packets having a destination IP address of either the client computer or the server computer as received in the computer configured as the SMTP transparent relay, the computer configured as the SMTP transparent relay including a communications interface in promiscuous mode for each of the client computer and the server computer;
• monitoring the communication session between the client computer and the server computer by checking SMTP commands sent by the client computer to the server computer and responses by the server computer to the SMTP commands sent by the client computer at different states of the SMTP to check for network security policy violations;
• and
• relaying communications between the client computer and the server computer when the monitoring of the communication session does not indicate a network security policy violation.