Monday, June 22, 2009

SMTP Packet Inspection

I have seen this a number of times now when you telnet a SMTP server you get this:

220 ********************************************************

This is caused by SMTP Packet inspection on the router's or layer 3 switches. Speak to your network engineer to turn this off.

If you have packet inspection on SMTP, but your relaying ESMTP ie EHLO and not HELO, it will not read write and data will not get accross. I have seen problems with mail flow between exchange 2007 and 2003 because of this. Exchange 2003 if EHLO fails it will use HELO to relay (standard SMTP). Exchange 2007 likes to use just ESMTP between routing group connectors however you can configure this to use standard SMTP if you like.

Overall I recommend turning SMTP packet inspection OFF on your Cisco gear as it causes nothing but issues.

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