On Fri, Oct 16, 2020 at 02:37:04PM -0400, Demi M. Obenour wrote:
> > Unless there's a particularly good reason why you believe that OpenSMTPD
> > would do better than Postfix in bulk mail delivery performance, it is not
> > helpful to recommend it here.
>
> I misunderstood your previous message, sorry. I interpreted it as a
> statement that Postfix struggles with very large mail queues, and I
> know OpenSMTPD does not.
There is no MTA which is able to retry an arbitrarily large queue in the
face of remote tempfailures without the retry times stretching out to
unnacceptably large values. This is a mathematical fact. Given that
the output rate is bounded, the time taken to process a large backlog
grows with the size of the backlog.
The practical limit to the deferred queue size is therefore ~2 days of
throughput, and depends heavily on the per-delivery latency. If
delivery failures are slow (tarpitting or otherwise slow destinations)
the impact is greater.
There is no magic that can make OpenSMTPD immune to the laws of
arithmetic.
Otherwise, with appriate choices of hash_queue_depth and
hash_queue_names, Postfix handles backlogs in the low millions
of messages, because anything much higher simply will not get
processed quickly enough in a reasonable time.
--
Viktor.
