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Cisco ASA drops email (SMTP) from some domains

Posted on 2010-11-11
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Last Modified: 2012-05-10
We are missing some emails from Domains.  I have enclosed the logs for one paticular domain that can not send back to us.


Built inbound TCP connection 14677106 for outside: xxx.xxx.250.xx/59339 (xxx.xxx.250.99/59339) to inside:xxx.x.x.xx/25 (XX.151.25.XX/25)


Deny TCP (no connection) from xxx.xxx.250.99/59339 to XX.151.25.XX/25 flags ACK  on interface outside
Deny TCP (no connection) from xxx.xxx.250.99/59339 to XX.151.25.XX/25 flags ACK  on interface outside
Deny TCP (no connection) from xxx.xxx.250.99/59339 to XX.151.25.XX/25 flags PSH ACK  on interface outside
Deny TCP (no connection) from xxx.xxx.250.99/59339 to XX.151.25.XX/25 flags ACK  on interface outside
Deny TCP (no connection) from xxx.xxx.250.99/59339 to XX.151.25.XX/25  flags ACK  on interface outside
Deny TCP (no connection) from xxx.xxx.250.99/59339 to XX.151.25.XX/25 flags ACK  on interface outside

Not sure why some are coming through and others are not.
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Question by:Tech_guy
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EndureKona earned 250 total points
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by:Alan Hardisty
Alan Hardisty earned 250 total points
ID: 34116702
The CISCO ASA will have ESMTP Inspect / Inspect ESMTP (equivalent of SMTP Fixup) - this is well known to cause mail-flow issues and should be disabled on your ASA device.

If you can't find SMTP Fixup - look for ESMTP Inspect and disable it.
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