Kristjan Nii:
> Thank you for your response!
> I viewed the some emails in the queue and did not see DKIM signatures in
> them. Also, our network guys confirmed, that ASA version is 7.3, which
> should be bug-free.
> Any other ideas or things I should/could check and test?
Other issues may have to do with broken IP path MTU discovery
(which an be worked around by turning that off in the sender's
TCP/IP stack), or broken window scaling, or some other bug.
This can be diagnosed by looking at a packet recording.
And one should not exclude the possibility that your email
is blocked by some firewalling rule, which will have te same
result that packets are silently discarded.
Wietse