On Wed, Mar 13, 2024 at 04:29:19PM +0000, Colin McKinnon via Postfix-users
wrote:
> In my previous question [1] Viktor Dukhovni suggested
>
> > you could use a policy service to impose rate limits per SASL login, or
> > sender address
>
> as a means of preventing active queue congestion.
http://www.postfix.org/SMTPD_POLICY_README.html
> This took me down a bit of a rabbit hole looking at SMTP Access Policy
> delegation and tcp_tables.
You don't need "tcp_tables" here, the protocol for policy services is
described in:
http://www.postfix.org/SMTPD_POLICY_README.html#protocol
There are multiple examples of existing policy services.
> However I have not managed to find much
> (ANY???!!!) information on what the server responses should look like.
See the protocol definition linked above.
> Although I don't yet know exactly what they look like, I have only seen
> mention of accepting or rejecting emails at submission using SMTP Access
> Policy delegation.
Or deferring, with 4XX, if submission is from an MTA that can queue for
a later retry.
> I really want to be able to generate, on a per message basis, the
> behaviours that I currently have statically defined in a transport map.
> These are:
>
> (condition1) customtransport:
Unclear how this avoids active queue congestion.
> (condition2) smtp:[othernode]
Or this. If a much larger queue size limit and much larger delivery
agent limit don't solve the problem, you need backpressure to reduce
the input rate, which tweaking output parameters will not achieve,
unless somehow you get much better latency for some destinations (which
is fine to do of course).
--
Viktor.
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