Jul 19 13:40:39 mx31 postfix-p25/smtpd[96635]: NOQUEUE:
client=mail.rosedale.ca[66.135.118.147]
Jul 19 13:40:39 mx31 postfix-p25/smtpd[96635]: lost connection after
DATA (0 bytes) from mail.rosedale.ca[66.135.118.147]
Jul 19 13:40:39 mx31 postfix-p25/smtpd[96635]: disconnect from
mail.rosedale.ca[66.135.118.147] ehlo=1 mail=1 rcpt=1 data=0/1
commands=3/4
The sending client is encountering networking issues. Unrelated
to Postfix or TLS. Your new systems may have enabled TCP window
scaling or ECN, or other TCP features that are giving the sending
system indigestion. Or just a vanilla MTU issue. You could try
to disable window scaling, which makes data transfer slower for
senders with a high bandwidth delay product, but email is generally
tolerant of a few seconds to minutes of extra delay.
It could help to allow icmp type 3 code 4 (Destination Unreachable
Fragmentation Needed) between the machines.
Best regards
Jan
