On Sat, Jun 29, 2024 at 12:00:43AM -0400, John C Klensin wrote:
> > For context, absolutely none of the major email delivery providers
> > (AWS SES, SendGrid, Mailgun, Postmark, SMTP_com, etc.) support ipv6.
> >...
That of course has nothing to do with SMTP (the protocol) as such.
There are a few plausible tangential reasons:
- Some receiving systems are more strict in what they're willing
to accept via IPv6 rather than IPv4. As a consequence, one can
choose to try to jump through more hoops, or just be sure to send
via IPv4. [ The extra scrutiny may be because with so much
address space in IPv6, IP reputation is perhaps less effective,
without additional signals. ]
- IPv4 works well enough that the incentives aren't there to invest
scarce human cyles into bringing up outbound services on IPv6.
Meanwhile, major MTAs have had mature IPv6 support too long go to
remember [ O.K. ~20 years in the case of Postfix. ]
The issues are non-technical at this point, some major receiving systems
need to make it more (rather than less) attractive to send over IPv6.
--
Viktor.
