XFOR: Cannot Reply to Messages Through a Cisco PIX Firewall

If you send a message from one Microsoft Exchange Server computer to another through the Internet Mail Service, and then attempt to reply to the message, the reply may not be sent successfully. This problem occurs when the two servers are connected through a Cisco PIX Firewall on which the Mail Guard feature is enabled.

To work around this problem, disable the Mail Guard feature on the Cisco PIX Firewall. For additional information, contact Cisco.

For information about how to contact Cisco, query in the Knowledge Base for one of the following articles:

Mail Guard is a feature that allows messages to be transferred directly to an internal e-mail host, eliminating the need for an e-mail relay host. Mail Guard allows connections to an internal e-mail host through Transport Control Protocol (TCP) port 25 only. It logs all Simple Mail Transfer Protocol (SMTP) activity and allows only the minimum SMTP server commands found in Request for Comments (RFC) 821, Section 4.5.1.

PIX Firewalls are manufactured by Cisco, a vendor independent of Microsoft; we make no warranty, implied or otherwise, regarding these products' performance or reliability.