[devtalk] [wdvltalk] New list bounces - suspected DNS problem

[David Precious]

David Precious wrote:
> After some investigation, I *think* I see what's going on.
[...]
> Now, I *think* this is a DNS configuration issue; it seems I don't have 
> MX records for lists.preshweb.co.uk configured, lists.preshweb.co.uk is 
> instead a CNAME to lyla.preshweb.co.uk (lyla being the name of the 
> machine actually responsible for hosting lists.preshweb.co.uk).
[...]
> However, for others, it seems as though your client is seeing that 
> lists.preshweb.co.uk is a CNAME to lyla.preshweb.co.uk, and silently 
> re-addressing the mail to devtalk at lyla.preshweb.co.uk instead of 
> devtalk at lists.preshweb.co.uk.

OK, I think I was on the right lines; it seems that Sendmail is 
retarded, and "expands" cnames, modifying the address you sent your mail 
to, which seems stupid.

Example:
http://www.phwinfo.com/forum/comp-mail-sendmail/207463-turning-off-domain-name-canonifying.html


So, my setup was perfectly valid, but Sendmail MTAs configured in 
certain ways would exhibit brain damage and munge the recipient address.

That's why we were seeing the problem with some accounts, but not 
others; if there was a Sendmail MTA with this behaviour somewhere 
between you and the list server, then it would happen.

To fix this, I've added an MX record for lists.preshweb.co.uk (the CNAME 
is still there, which contravenes a "should not" in RFC 1034, but should 
not be a problem).

Being DNS, it's quite possible the record is cached in places, and you 
may still see this weird behaviour for a while.

Cheers

Dave P