Why has SMTP stopped responding or gone slow?

Question

If you TELNET to the SMTP port (25), you find that a connection is established but no SMTP banner will be
presented. It may take several minutes before the usual SMTP banner is displayed.

Answer

From 1-Aug-01, MAPS has become a subscription service.

If you are using MAPS for DNSBL, and you have not taken out a subscription with MAPS then your SMTP will appear to stop responding to SMTP connections. In fact, there is a delay of 30 seconds for each DNSBL server check.

GMS Anti-Spam is designed so that if a DNSBL server is down it will ignore the server and continue any other checks as usual. Each check takes 30 seconds before it is aborted and the next check starts.

Solutions:

1. Remove the MAPS servers from the DNSBL checks.
2. Purchase a plan from MAPS at http://www.mail-abuse.org.

NOTE: This change has affected other MTAs such as PMDF, sendmail, etc.

See Also:

• Cisco Routers causing SMTP time outs
• Why does my SMTP service suddenly stop?
• GMS and Cisco PIX firewalls

Keywords:DNSBL MAPS SMTP