Re: [ipv6-wg] Real-world IPv6 SMTP experience

[Tim Chown <]

On Wed, Dec 21, 2005 at 04:13:04PM +0100, Stig Venaas wrote:
> On Wed, Dec 21, 2005 at 04:08:16PM +0100, Florian Weimer wrote:
> > * Gert Doering:
> > 
> > > So if I understand this correctly, having a v4-only backup MX should
> > > solve all problems commonly experienced?
> > 
> > As far as I know, the primary MX needs an A record (to satisfy
> > Sendmail), and there needs to be a MX which has an A record only (and
> > no AAAA or A6 record; this is done to satisfy Exim installations).  My
> > initial question to this list was whether if you can do this with just
> > a single IPv4 address, and still prefer IPv6 over IPv4 (assuming that
> > IPv6-capable hosts prefer IPv6 hosts over IPv4 hosts if they have the
> > same priority).
> 
> At least at uninett.no this is done with only one IPv4 address. The
> primary MX has both A and AAAA, and the secondary is only A, but with
> same IPv4 address as primary. Well, you can check mx's for uninett.no
> yourself.
> 
> I know several sites that have both A and AAAA for all MXs. It doesn't
> sound safe to me, but I assume it can't be that problematic then...?

Like Gert and Jeroen, we do that, and have not had complaints of failed
or problematic email (and have done it for a long time).   That's on a 
domain handling maybe 100K mails a day.   

-- 
Tim/::1