On Sun, Oct 10, 2010 at 09:25:38PM +0100, Mike Cardwell wrote:
> On 10/10/2010 19:41, Matthias-Christian Ott wrote:
>
> >> I recently got notified from a mailing list which is mangaged with
> >> ezmlm that E-Mails could not be delivered because my mail server
> >> rejected them. It turned out that the SMTP server or ezmlm itself
> >> rewrote the recipient of the envelope from bob@??? to
> >> bob@???, because example.com was a CNAME for b.example.com.
> >>
> >> Is such rewriting compliant with any standard (according to the
> >> rejectlog no other E-Mails got rejected for this reason)?
> >
> > As more E-Mails come in, it seems very likely that some SMTP servers
> > got confused by the CNAME and as far as I can tell from the logs
> > didn't even try to deliver the E-Mails to my server.
>
> If your MX record is pointing at a CNAME, then your DNS is broken. MX
> records are not allowed to point at CNAMEs, they're only allowed to
> point at A records.
I think this was not the problem (maybe the problem statement was
ambiguous). My DNS configuration was as follows:
example.com. IN NS 198.51.100.1
example.com. IN NS 203.0.113.1
on the nameservers I had the following:
example.com. IN CNAME b.example.com.
example.com. IN MX 10 mx.example.com.
b.example.com. IN A 198.51.100.2
mx.example.com. IN A 198.51.100.3
According to RFC 1912 there can't be other RRs if there's already a
CNAME. It seems some SMTP servers followed the DNS RFC very closely and
didn't send E-Mails at all. But this doesn't explain why that particular
SMTP server rewrote the recipient (after I added a transitional MX
record for b.example.com ebay.com did the same).
Regards,
Matthias-Christian
