Difference between revisions of "SMTP Fixup Issue"
From Roaring Penguin
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| − | This | + | This may also be referred to as SMTP Inspection and is a feature on Cisco firewalls. Unfortunately it causes what are often hard to diagnose intermittent blocking of email passing through the firewall and is considered a useless anti-spam feature by most. The following article contains more detail: |
https://blogs.it.ox.ac.uk/networks/2009/11/26/cisco-firewall-smtp-fixup-considered-harmful/ | https://blogs.it.ox.ac.uk/networks/2009/11/26/cisco-firewall-smtp-fixup-considered-harmful/ | ||
Latest revision as of 12:23, 15 March 2016
This may also be referred to as SMTP Inspection and is a feature on Cisco firewalls. Unfortunately it causes what are often hard to diagnose intermittent blocking of email passing through the firewall and is considered a useless anti-spam feature by most. The following article contains more detail:
https://blogs.it.ox.ac.uk/networks/2009/11/26/cisco-firewall-smtp-fixup-considered-harmful/
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 server.at.some.domain 25 Trying 1.2.3.4... Connected to server.at.some.domain. 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.
