SMTP Fixup Issue

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This is also referred to as SMTP Inspection and is a feature on Cisco firewalls. Unfortunately it causes what are often hard to diagnose blocking of email passing through the firewall and is considered a useless anti-spam feature by most. The following article contains more detail:

To determine if this feature is in the mail delivery path for your mail server go to an external computer and open a terminal window. Then telnet to your mail server on port 25 as shown below:

  root@colo4(~)# telnet 25
  Connected to
  Escape character is '^]'.
  220 *************************************************************************************************

The long line of "*" is the indicator of the feature being in place. We strongly recommend that the feature be disabled on the firewall.