>14614 SMTP>> 220 mail.XXXXXXX.it ESMTP Exim 4.60 Mon, 01 Sep 2008 14:44:01
+0200
>14614 Process 14614 is ready for new message
>14614 smtp_setup_msg entered
>14614 SMTP>> 421 mail.XXXXXXX.it lost input connection
>14614 LOG: smtp_connection MAIN
>14614 SMTP connection from cp-out4.libero.it [212.52.84.104] lost
Is there a IPSEC VPN in between. As this might also be a symptom of failed
path MTU discovery. Where your machine wants 1500 byte TCP/IP-packets, but
because of failed detection (probably ICMP packet filtering) sender cannot
send big packets and those get dropped by network.
Additional test could be dropping MTU to 1400 bytes and see what happens.
More info (no need to cut&paste here):
http://en.wikipedia.org/wiki/Maximum_transmission_unit
"Path MTU discovery"
