Frank Ellermann wrote:
Bill Manning wrote:
example.com. soa (
mailhost aaaa fe80::21a:92ff:fe99:2ab1
is what i am using today.
In that case adding an MX record pointing to mailhost
or not is perfectly irrelevant from an IPv4-only POV:
IPv4-only users cannot reach your AAAA, therefore they
better reject mails claiming to be from any(_at_)example(_dot_)com
at their border for obvious reasons.
uh, no. IPv4-only hosts can see the AAAA record even if they can't
directly send mail to that address. and there's no reason ("obvious" or
otherwise) why a MTA should reject mail from a host just because that
MTA can't directly route to it - since there's nothing that requires a
user to use the same MTA for outbound mail that is used to receive
inbound mail. (granted, lots of really really stupid things are done in
the name of spam filtering that make no more sense than this, but
they're not "obvious" - they're just stupid).
of course, as a practical matter, any domain for which mail eventually
ends up in an IPv6-only world is going to need to have at least one MX
pointing to a IPv4-capable host, until IPv6 becomes ubiquitous or very
nearly so. so the example above only makes sense in a world where IPv6
is ubiquitous - or perhaps, where the owner of example.com wants to
gauge the degree of IPv6 support for outgoing mail.
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