Re: NDPMon

[Stephane Bortzmeyer <bortzmeyer@nic.fr>]

On Tue, Oct 03, 2006 at 09:12:27AM -0400,
 Anthony DeRobertis <anthony@derobert.net> wrote 
 a message of 22 lines which said:

>     $ host -t MX example.com
>     example.com has no MX record
> 
> So, the mail should bounce.

Wrong. Read RFC 2821 :

   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. 

...

   The lookup first attempts to locate an MX
   record associated with the name.  If a CNAME record is found instead,
   the resulting name is processed as if it were the initial name.  If
   no MX records are found, but an A RR is found, the A RR is treated as
   if it was associated with an implicit MX RR, with a preference of 0,
   pointing to that host.

> Well, some mailers then send to the A record so maybe...

They MUST, if they are compliant with the SMTP standard.