[TriLUG] Re: sendmail, mailman, and mm-handler

[Lance A. Brown]

 From http://www.zvon.org/tmRFC/RFC2821/Output/chapter5.html

Once an SMTP client lexically identifies a domain to which mail will be 
delivered for processing (as described in sections 3.6 and 3.7), a DNS 
lookup MUST be performed to resolve the domain name [22 
<http://www.zvon.org/tmRFC/RFC2821/Output/chapter9.html#22>]. The names 
are expected to be fully-qualified domain names (FQDNs): mechanisms for 
inferring FQDNs from partial names or local aliases are outside of this 
specification and, due to a history of problems, are generally 
discouraged. 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. If MX records are present, but none of them are usable, 
this situation MUST be reported as an error.

So, if you have no MX records, the MTA is supposed to check for an A 
record and send it to the resulting IP address.  If you have MX records, 
they better be able to accept your mail or the message will get bounced.

--[Lance]


Jon Carnes wrote:

>You are correct that a machine does not need an MX record to receive
>mail sent to that machine; however, since Ryan's server is attempting to
>send his local mail off of the machine (rather than accept it locally)
>there is clearly a problem of some sort. 
>
>In my dealing with folks on the mailman list, a common problem is that
>they *have* mx records, and they are set incorrectly. 
>
>So if you have a suggestion that might help Ryan, lets hear it.
>
>Jon Carnes
>
>On Fri, 2003-08-22 at 09:30, Christopher L Merrill wrote:
>  
>
>>rasch at raschnet.com wrote:
>>    
>>
>>>Some MTA's won't deliver to a domain without an MX. Why not have one?
>>>      
>>>
>>Really?  Which ones?
>>
>>According to dyndns.org:
>>    
>>
>>>Many people think that you need an MX record to receive mail. This is incorrect. 
>>>In the absence of an MX, mail to a machine (for example, mail to 
>>>@who-needs-an-mx.dyndns.org or @yourcustomdns.com) will be handled by that
>>>machine (in the case of my example, the machine at who-needs-an-mx.dyndns.org
>>>or at yourcustomdns.com). This is the behavior that most people running mail
>>>servers on their home machines want. For this reason, we do not recommend that
>>>users wanting a basic mail configuration set up an MX. It is not necessary, and
>>>it is possible to make mistakes in the MX record that will cause mail to end up
>>>somewhere else.
>>>      
>>>
>>Who's right?
>>
>>C
>>
>>
>>-------------------------------------------------------------------------
>>Chris Merrill                      |  http://webperformanceinc.com
>>Web Performance Inc.               |  http://webperformancemonitoring.net
>>
>>Website Load Testing, Stress Testing, and Performance Monitoring Software
>>-------------------------------------------------------------------------
>>    
>>
>
>  
>

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