(no subject)

[Kevin Darcy]

Chris Meadors wrote:

> On Tue, 6 Feb 2001, Joseph S D Yao wrote:
>
> > > Some mail servers will fall back to using the A record, but they are by no
> > > means required to, and in my opinion doing so is incorrect.
> >
> > Strangely, your opinion is in direct conflict with the RFCs.  They are
> > required to.
>
> I do stand corrected.  After I made my post, I actually sought out the
> RFCs and found I had erred.  I probally should have done this in the
> oppisite order.
>
> So, let my pose this less than hypothethical situation.
>
> A site operator does define an MX, and it points to a hostname not an IP
> as required by an RFC.  But the hostname it points to does not resolve to
> an IP.
>
> What should the mailer do?

RFC 974 doesn't really say. So the default is "it's implementation dependent".
sendmail, for instance, just bounces the message with "host not found" in that
situation, even if there is an A record that could be used. The reasoning,
I assume, is that if the MX record exists, we presume that the name's owner
wanted that to be used instead of the A record, for purposes of mail routing.


- Kevin