On Mon, Oct 28, 2024 at 06:17:56PM -0400, Wietse Venema via Postfix-users wrote:
> > My problem is that I have to slow down the sending rate to domain1, but
> > in the same time I need to segregate (send out on different IP address)
> > based on sender address.
> >
> > So, as I understand this is possible only with multi-instance?
>
> main.cf:
> # Limitation: this setting is overruled with FILTER om access map
> # or header/body_checks.
> smtpd_sender_restrictions = inline:{
> { u...@example.com = FILTER smtpb: } }
>
> A less hackey solution would require a transport policy service,
> kind of like check_policy_service for the scheduler.
Or multiple instances with sender_dependent routing in the front-end
instance sometimes bypassing the default back-end instance which ignores
sender addresses and routes by recipient.
This avoids problems if "u...@example.com" happens to send mail to a
local address, that should not be sent via "smtpb".
Postfix sensibly prioritises choosing transports by recipient rather
than sender when explicit non-default routing is available. The OP's
case of carving out very special exceptions does not have a simple
solution.
What's "missing" is a way to say that an explicit transport selected
for a recipient is still in some sense a lower priority "default"
transport that a sender-dependent transport might override. This
would include custom delivery channels to remote destinations used
only for traffic shaping, but not deliveries to local or relay
recipients.
One way to do this would be designate additional transports as
being essentially secondary "default" transports.
default_transport = smtp
secondary_default_transports = smtpa
in which case sender_dependent_default_transport would override "smtp"
and "smtpa", but not "relay", "local", or "virtual", ...
--
Viktor.
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