On Tue, Mar 26, 2024 at 02:20:55PM -0400, Wietse Venema via Postfix-users wrote:
> Viktor Dukhovni via Postfix-users:
> > That's fine, the SRV records can be keyed by destination domain.
>
> Locally-managed SRV records, keyed by the final destination domain
> name, to select a local relay host?
Yes. The only tricky part is getting the queries to go to the right
zone, which requires appending a suffix to the nexthop domain.
So a socketmap transport lookup that maps:
foo.example -> dnslb:foo.example.dnslb.local:smtp
and a custom DNS authoritative server handling "dnslb.local" (or other
suitable suffix).
To have separate load-balanced transport per-sender, one could have
sender_dependent_transport:
example.com dnslb1
example.net dnslb2
...
And the socketmap would then leave the transport unchanged, and tweak
just the nexthop:
foo.example -> :foo.example.dnslb.local:smtp
Encoding both the sender domain and the recipient domain into a single
lookup, as with the policy service, is otherwise difficult, so if
all mail is single-recipient, one might use FILTER, and still SRV
lookups on the backend:
sender domain: belongs to client1
recipient = ...@example.net
action = FILTER dnslb:example.net.client1.dnsbl.local
Then the DNS server can parse out the destination and client id and do
as it pleases.
--
Viktor.
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