On Thu, May 27, 2021 at 01:16:22PM -0400, Eric Germann wrote:
> I have a mailing list I’m trying to join to which is v4/v6 enabled.
> My v4 has a proper PTR record. My v6 does not currently and I’m going
> round and round with AWS to get it updated.
>
> Is there a way in Postfix to force delivery for a particular host or
> domain to deliver over v4 without playing parlor games with DNS (ala
> the Netflix workaround for v6 on tunnels)
Given that IPv6 address has no PTR, you should not use IPv6 for *any*
destinations. For that, just configure:
smtp unix - - n - - smtp
-o inet_protocols=ipv4
If at some point later you really have a compelling use-case for
making this destination-specific, add:
smtpv4 unix - - n - - smtp
-o inet_protocols=ipv4
and use it with the transport table for the destination domains in
question. Note, transport selection happens *before* MX host lookup, so
the transport setting is per destination domain, not per MX host.
To suppress v6 for a particular host, you'd need to filter out its IPv6
addresses via smtp_dns_reply_filter.
--
Viktor.
