We have been running (fairly successfully) a split domain with two MTA's. The ZCS MTA, and an external "primary" (our old sendmail mailhub). Inbound mail would route to the sendmail MTA, which would then pass mail to our ZCS MTA.

Recently, however, It seems a problem has cropped up for us after we upgraded to ZCS 4.5.9 a few weeks ago. Some inbound email, mostly originating from gmail, is being held up between our two MTA's. It has the feeling that something was enabled in the ZCS that I can not seem to find, as now it is rejecting gmail.com messages.

Code:
Nov 20 13:53:21 MTA postfix/smtpd[11393]: connect from smtp.MYDOMAIN.com[VAL.ID.IP.ADR]
Nov 20 13:53:21 MTA postfix/smtpd[11393]: B3D552FB0823: client=smtp.MYDOMAIN.com[VAL.ID.IP.ADR]
Nov 20 13:53:21 MTA postfix/smtpd[11393]: lost connection after DATA from smtp.MYDOMAIN.com[VAL.ID.IP.ADR]
Nov 20 13:53:21 MTA postfix/smtpd[11393]: disconnect from smtp.MYDOMAIN.com[VAL.ID.IP.ADR]
Now, I have turned off all of the checks that postfix attempts, and that does not seem to fix it. Is anyone else seeing similar, almost random problems with different domains?