[ipv6-wg] Real-world IPv6 SMTP experience

[Florian Weimer <]

Hi,

is there any document that contrasts RFC 3974 with the real world?  I
try to create a set of MX RRs which includes an IPv6 MX host, does not
negatively impact reachability from v4-only hosts (or v6-enabled hosts
without v6 connectivity), prefers v6 over v4 when possible, and does
not waste any IPv4 addresses.

This is what I've come up with so far:

deneb.enyo.de.          172800  IN MX      9  v6.mail.enyo.de.
deneb.enyo.de.          172800  IN MX      10 v4.mail.enyo.de.

v6.mail.enyo.de.        172800  IN A       212.9.189.167
v6.mail.enyo.de.        172800  IN AAAA    2001:14b0:202:1::a7
v4.mail.enyo.de.        172800  IN A       212.9.189.167

The A RR of v6.mail is necessary because some broken anti-spam checks
reject mail from deneb.enyo.de if they cannot find an A record for the
primary MX.  The v4.mail MX host is needed because some MTAs suppress
A record lookup if they discover an AAAA record (even if there's no v6
connectivity available).

I wouldn't be too surprised when this setup leads to bouncing mail,
too. 8->

Florian