5.1.0 500-'Firewall Error' - Cisco Firewall or Cisco UC500

Ich hatte da ein blödes Problem bei einem Kunden :

Der Exchange 2007 Server kann manchmal mails nicht verschicken.

Jetzt habe ich nach langer Suche die mögliche Ursache gefunden !

Der Cisco Router ist schuld wie es scheint 

5.1.0 500-'Firewall Error'

Issue: Repeated Error: #500 Firewall Error ## -or- #5.0.0 smtp; 5.1.0 - Unknown address error 500-'Firewall Error' (delivery attempts: 0)> #SMTP# 

Cause: The Cisco firewall has a configuration entry like the following (it may have additional parameters specified after in addition to esmtp):

ip inspect 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. 

Please Note: If using CCA to apply, re-apply, resety or midify your Cisco firewall, this entry may be re-inserted by CCA and you will have to manually remove.

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 esmtp

Other people have seen this problem as well:
http://www.solutions.pro/email-server-generates-500-firewall-error-error-8/
http://nzschooltech.blogspot.com/2009/09/exchange-management-console-issue-on.html
http://mattlog.net/2008/12/31/exchange-2007-500-firewall-error/
http://clintboessen.blogspot.com/2009/11/510-500-firewall-error.html