why cisco firewall course exchange mail error?

Unanswered Question
Jul 13th, 2010

Followed the instruction below, it fixed bounce back mail issue. Why cisco firewall cause this problem?

Diagnostic information for administrators:

Generating server: <local Exchange server FQDN>

[email protected]
<remote SMTP server FQDN> #500 Firewall Error ##

CAUSE: The Cisco firewall has a configuration entry like the following (it may have additional parameters specified after <inspection-list-name> in addition to esmtp):

ip inspect name <inspection-list-name> esmtp

This problem occurs because of incompatibilities or restrictions caused by the Cisco firewall configuration. It is more likely to occur if you are sending an email to multiple recipients or using a distribution list in Exchange.

FIX: Disable this entry in the Cisco firewall configuration by inserting the word “no” at the beginning of the line as shown, so that it should now read something like

no ip inspect name <inspection-list-name> esmtp

I have this problem too.
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Nagaraja Thanthry Tue, 07/13/2010 - 17:57


The SMTP inspection is used to protect the SMTP server from any attacks. It will ensure that only certain commands are issued to the server and the commands issued are in proper syntax. If the client server is a legacy system, some of the commands used by the client server may not be compatible with the ESMTP inspection causing break in the communication. Here is a detailed explanation of the ESMTP inspection functionality.


Hope this helps.




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