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From: Wietse Venema on 28 May 2010 09:06
Ioannis Tsouvalas:
> 451 Requested action aborted: local error in processing

This is not a Postfix error mesage. It is an error in a non-Postfix MTA.
Please do not shoot the messenger.

> 451 Temporary local problem - please try later

This is not a Postfix error message. It is an error in a non-Postfix MTA.
Please do not shoot the messenger.

> 421 4.4.1 Connection timed out (in reply to end of DATA command)

This is not a Postfix error message. It is an error in a non-Postfix MTA.
Please do not shoot the messenger.

> said: 421 4.4.2 mxfront39.mail.yandex.net Error: timeout exceeded (in reply
> to end of DATA command)

This is an error message from a remote system.
Please do not shoot the messenger.

> (lost connection with mx1.mail.eu.yahoo.com[77.238.177.9] while sending end
> of data -- message may be sent more than once)

Here, Postfix lost the connection with Yahoo. This is "not unusual".

All these errors happen outside Postfix. You're better off spending the
energy on other things.

Wietse

From: Wietse Venema on 28 May 2010 10:37
Ioannis Tsouvalas:
> >
> >Ioannis Tsouvalas:
> >> 451 Requested action aborted: local error in processing
> >> 451 Temporary local problem - please try later

These you can do nothing about, except perhaps retry when the remote
system is under less stress.

> >> 421 4.4.1 Connection timed out (in reply to end of DATA command)
> >> 421 4.4.2 mxfront39.mail.yandex.net Error: timeout exceeded (in
> >> reply to end of DATA command)

These could be a network-level problem such as broken IP path MTU
discovery, or TCP options that are mis-implemented by an and system
or by an intermediate system (such as a cheap firewall).

There is some 12 years of discussion archived on-line that covers
IP path MTU problems, and some 5 years for mis-implemented TCP
options (Sack, Wscale, ...). I see that you have already turned
off some of those.

This can be debugged by capturing network packets and making sense
of the flags, windows, ACK offsets, and retransmissions. I have
done that in earlier years but can no longer afford the time.

Wietse

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