problem: Mail server users may get a delivery delayed message or system administrators may see a delay notice in their logs.  The delay error is 421 Timeout or 451 Cannot connect.  The messages may be delayed to the point where queue expiration occurs and the message is rejected.  

This can happen if you use "Inspect ESMTP" on your ASA device. Disabling this will allow these connections through unobstructed.

To remove fixup/Inspect ESMTP...

If you have access to ASDM then:


Configuration --> Service Policy Rules -->  General/Global Policy --> Edit ---> Rule Actions --> Untick ESMTP

Click OK --> Apply --> Save


If you do not have ASDM, then the PIX CLI is:

en

{password}

conf t

no fixup protocol smtp 25

{ctrl+z}

wr me

exit