Peter J. Holzer writes:
On 2008-04-04 17:30:29 -0400, Robert A. Rosenberg wrote:
RFC 3974
[...]
It, BTW, REQUIRES an MX if there are any IPv6 MTAs and only supports
A-Fallback in the absence of an MX
No.
"For the transition period, all mail domains should have MX records such
that MX targets with IPv4 and IPv6 addresses exist"?
It also states that in the presence of an MX containing IPv6 address
references, an IPv4-Only stack should ignore the IPv6 addresses
Yes, of course. It cannot reach them anyway. Just as IPv6-only hosts
can ignore A records since they cannot reach them either.
An IPv6-only host must use the presence/absence of A records to generate
the DSN. The DSN status code is 5.1.2 if there's no A and 5.4.x if
there is an A but no way to reach it (ie. no configured relay).
Arnt