Wietse Venema via Postfix-users:
> Bill Sommerfeld via Postfix-users:
> > About three years ago there was a thread on postfix-users ("Comcast 421
> > throttling multiple recipients") discussing a low-traffic site having
> > difficulties sending to multiple recipients at comcast in a single smtp
> > session. The thread starts here:
> >
> > https://www.mail-archive.com/postfix-users@postfix.org/msg88394.html
> >
> > and it appears to have died out without consensus on what was going on.
> >
> > I believe I understand what the original poster was seeing because it
> > just happened to me. Having a way to disable the special per-recipient
> > behavior when ${transport}_destination_recipient_limit=1 would be very
> > useful in working around quirky receiver like this.
>
> Would it be sufficient to never send more than 1 recipient per
> mesage, thus never trigger their temporary "block all mail" strategy,
> and avoid the need for the kludges described here?
I think that the 'slow' example should handle this:
/etc/postfix/master.cf:
# Don't immediately try an alternate MX after 4xx server response.
slow unix - - - - 1 smtp
-o { smtp_mx_session_limit = 1 }
# Execute "postmap hash:/etc/postfix/transport" after editing the file,
# then "postfix reload".
/etc/postfix/transport:
comcast.net slow:
/etc/postfix/main.cf:
transport_maps = hash:/etc/postfix/transport
# Don't send multi-recipient messages over the 'slow' transport.
slow_destination_recipient_limit = 1
# Don't send parallel messages over the 'slow' transport.
slow_destination_concurrency_limit = 1
# Don't send messages back to back over the 'slow' transport.
slow_destination_rate_delay = 1
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