Oddball DNS issue: won't resolve hostname alone.

Peter McNabb peter at mcnabbs.org
Mon Dec 17 13:32:15 MST 2007


On Dec 17, 2007, at 12:45 PM, Charles Curley wrote:

> On Mon, Dec 17, 2007 at 10:52:45AM -0700, Shane Hathaway wrote:
>> Charles Curley wrote:
>>> I set up bind9 on an Ubuntu box several weeks ago. Now, email on two
>>> Ubuntu machines is broken. I get, e.g.
>>>
>>> Dec 17 09:50:58 phoenix postfix/smtp[436]: 08D2A16A0E4:
>>> to=<ccurley at charlesc>, orig_to=<root>, relay=none, delay=8152,
>>> delays=8142/0.01/10/0, dsn=4.4.3, status=deferred (Host or domain
>>> name not found. Name service error for name=charlesc type=A: Host  
>>> not
>>> found, try again)
>>
>> This should work once "dig mx charlesc" works on 192.168.1.3.   
>> Postfix
>> looks first for an MX record rather than an A record.
>
> It does? I've never had an MX record before. And failing an MX record,
> shouldn't it then try for an A record?

Yes. Er, well, that's how the RFC says it should work. A quick glance  
at the postfix source confirms that it does work this way. :)

 From RFC 2821:
"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.  If one or more MX RRs are found for a given name, SMTP  
systems MUST NOT utilize any A RRs associated with that name unless  
they are located using the MX RRs; the "implicit MX" rule above  
applies only if there are no MX records present."

-peter



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