[TAG] A couple of questions regarding Mail policy

[Rick Moen]

Quoting Jay R. Ashworth (jra at baylink.com):

> > Everyone else considers such a host to have an implied MX record
> > with priority level zero.  Fortunately, I'm pretty sure all MTA
> > authors assume that, even Prof. Bernstein.
> 
> Doesn't 2821 or 2 explicitly say it these days?

In RFC2821:

3.6 Domains

   Only resolvable, fully-qualified, domain names (FQDNs) are permitted
   when domain names are used in SMTP.  In other words, names that can
   be resolved to MX RRs or A RRs (as discussed in section 5) are
   permitted, as are CNAME RRs whose targets can be resolved, in turn,
   to MX or A RRs. [...]

However, if you're one of the aforementioned obsessive-compulsives, you
might object that IETF still has RFC2821 in "standards track" status, 
which means it hasn't yet been formally adopted.

Reflecting further, I'm not 100% sure about whether Prof. Bernstein,
indeed, went with consensus on this one.  Certainly, the behaviour you
say has been attributed to his code on this matter would be in character
for something written by him.

In any event, DNS admins would probably be best advised to make _sure_
there's a valid MX record for any host running an MTA on the public Net,
just to be sure.

-- 
Cheers,                                        "He who hesitates is frost."
Rick Moen                                                 -- Inuit proverb
rick at linuxmafia.com