I would have to agree with the multiple connections == bad neighbour behaviour
(if this is true).
I might encourage re-ordering of sends to have parallel, per-MX queues ...
msg1 -> mx1 (in progress)
msg2 -> mx2 (start another process)
msg3 -> mx1 (queue and send on same connection as #1 when #1 is done)
msg4 -> mx3 (start another process)
msg5 -> mx2 (queue and send on same connection as #2 when #2 is done)
> ------------ HERE IS WHAT ORBS.ORG SAID ABOUT QMAIL: ------------
>
> Kick Qmail's author.
>
> To be honest, I regard qmail as a bit of a dog. It's great for mailing
> lists, but as a general purpose MTA it has too many bad habits.
>
> Apart from the accept, then process issue it also:
>
> Only sends one RCPT TO:<> per message, even if multiple recipients are at
> the same MX.
>
> Opens as many connections to a remote server as it can in order to deliver
> those individual messages in parallel.
>
> It results in temporary denial of service attacks and huge amounts of
> unnecessary bandwidth consumption. The program is designed around a
> mentality of "I will deliver the mail _now_, _no matter what_", instead of
> being a nice network neighbour and treating smtp as low priority data which
> is given sensible backoff algorithms.
