XFOR: Slow Banner Response from Internet Mail Service and an NDR Is Received

When you are using a host to connect to the Internet Mail Service, you must wait a long time (from five to twenty seconds) to receive the Simple Mail Transfer Protocol (SMTP) banner from Exchange Server 5.5. You may also receive a non-delivery response (NDR).

Slow banner response can be caused by any of the following reasons:

�	On a normal-to-heavily-used server that is running Exchange Server, the Performance Optimizer Wizard (Perfwiz.exe) has not been run since you installed Exchange Server 5.5.
�	A firewall or packet filtering software is delaying the banner response. In this case, you should perform telnet tests from both sides of all routers to measure the differences in banner response times.
�	If SMTP protocol logging is enabled, reverse-DNS lookups are performed on each incoming connection. This functionality affects computer performance.

Banner response can also be slow if the Exchange Server computer is querying a DNS server that is slow to respond.

For additional information, click the article number below to view the article in the Microsoft Knowledge Base: The NDR occurs because the connecting host has a lower wait threshold, and therfore may reset or retry the connection before the Internet Mail Service can display its banner. In this case, the host eventually sends an NDR for the original message back to the sender. However, most connecting hosts wait for the banner to be displayed before they submit messages to Exchange Server,

If slow banner response is caused by an unused Performance Optimizer Wizard, ensure that you run the Performance Optimizer Wizard after you install Exchange Server 5.5, any Exchange Server service pack, or any Exchange Server hotfix.

The Exchange Internet Mail Service listens on TCP port 25 for incoming SMTP messages from other hosts. When other hosts connect, they always wait for the banner response to ensure that Exchange Server is ready to accept a message.

For additional information about connecting and receiving the banner from the Internet Mail Service, click the article number below to view the article in the Microsoft Knowledge Base: