How you explain that we you apply in configuration command inspect esmtp with pix version 7(2)1, there is some trouble with mail.
I'm using exchange server.
Thank you a lot.
In 7.2.x (including the latest 7.2.2 interim releases) there are bugs related to SMTP/ESMTP inspection. PIX inspection engine drops connections if it finds a registered header name, as "Content-type", inside another header of any kind. This can happen if you use SpamAssassin and configure it to save reports inside e-mail header, or a remarkable case is Gmail which uses control headers containing other header names as keywords.
The problem is that RFCs do not forbid the use of a header name inside another header, but PIX/ASA Os 7.2.x incorrectly detects this behaviour as "malicious" because it sees a duplicate header. So it's the PIX that is wrong, not the messages. I opened a TAC case for this bug about one month ago.
The bug is now recognized as CSCsh33982, a level 2 bug. If you look in the Bug Toolkit you'll find the bug and you'll see that it is fixed in version 7.2(2)12 and 8.x. OS 7.2(2)12 is an interim release, but it is not public. Actually, today I installed it and I have found that the bug is not fully fixed: sometimes Gmail inserts two headers with the same keywords inside a message and the ASA/PIX still drops these messages. A new bug has been recognized: CSCsi01498.
So, at the moment, the only correct suggestion I can give you is to disable SMTP/EMSTP inspection if you use PIX/ASA OS 7.2.x. At least remove it for the traffic originated by or directed to your mail server if you don't want to loose messages.
Another note: serious modern e-mail servers allow you to configure security features for their SMTP service comparable or even better than those provided by PIX inspection. Even MS Exchange can be configured properly.