Message Submission Not Closed Properly

I recently noticed this pattern in my mail server logs:

May 10 23:51:32 lazarus postfix/submit/smtpd[26088]: connect from deepfield.scconsult.com[192.168.254.22] May 10 23:51:40 lazarus postfix/submit/smtpd[26088]: Anonymous TLS connection established from deepfield.scconsult.com[192.168.254.22]: TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits) May 10 23:51:41 lazarus postfix/submit/smtpd[26088]: 3b6vVP2bRDzxtKP: client=deepfield.scconsult.com[192.168.254.22], sasl_method=PLAIN, sasl_username=dad May 10 23:52:41 lazarus postfix/submit/smtpd[26088]: timeout after END-OF-MESSAGE from deepfield.scconsult.com[192.168.254.22] May 10 23:57:41 lazarus postfix/submit/smtpd[26088]: disconnect from deepfield.scconsult.com[192.168.254.22] May 11 16:32:23 lazarus postfix/submit/smtpd[46135]: connect from deepfield.scconsult.com[192.168.254.22] May 11 16:32:23 lazarus postfix/submit/smtpd[46135]: Anonymous TLS connection established from deepfield.scconsult.com[192.168.254.22]: TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits) May 11 16:32:24 lazarus postfix/submit/smtpd[46135]: 3b7Kj427X2zxxjD: client=deepfield.scconsult.com[192.168.254.22], sasl_method=PLAIN, sasl_username=dad May 11 16:33:24 lazarus postfix/submit/smtpd[46135]: timeout after END-OF-MESSAGE from deepfield.scconsult.com[192.168.254.22] May 11 16:38:24 lazarus postfix/submit/smtpd[46135]: disconnect from deepfield.scconsult.com[192.168.254.22]

Every time MM sends a message, it simply does nothing after the mail server sends its 200 reply to the message body. After a minute of nothing, the mail server acts like it got a RSET and after another 5 minutes of silence it drops the connection. MM never reports anything wrong and since the submission is complete as far as the server is concerned there is no delay in mail being sent.

Correct behavior would be for MM to send a QUIT command and close the session after getting the server reply to message data. In most cases the silent abandonment of the session is not a problem, but it can cause difficulties when a server has per-IP connection limits and multiple clients exist behind a shared NAT gateway.