Internal Mail DNS questions

Kevin Darcy kcd at daimlerchrysler.com
Sat Jul 2 01:56:44 UTC 2005


AVB wrote:

>I am having trouble sending mail internally from Server2 to Server1.
>Server2 sends mail fine to any other domain but just not internally.
>Server1 is our main Mail server and Server2 just sends message from our
>database application. Both servers are on the same W2K subnet and
>domain and I have one DNS server only for the internal machines. Our
>internal domain name is different than our Mail Domain name too so I'm
>not quite sure how MAIL DNS Queries operate in this regard.
>
>I set up both domain names in our internal DNS server with a MX and A
>record for the main mail server (server1) in the external domain and
>when I run
>
>Nslookup -q=mx server1.externaldomain.com I get:
>server1.externaldomain.com  192.x.x.x (internal IP)
>
>if I run NSlookup -q=mx externaldomain.com I get:
>responsible mail addr = admin.internaldomain.com
>
>if I delete the external domain in our internal dns server and run
>nslookup -q=mx server1.externaldomain.com I get the correct external IP
>
>and if I run nslookup -q=mx  externaldomain.com I get the correct
>server1.externaldomain.com and IP
>
>Not sure how to succesfully set up the DNS server for this. Anyone have
>any thoughts?  TIA!
>
What makes you think that your database app is doing MX lookups at all? 
Usually mail-enabled apps either a) deliver an SMTP message directly to 
a pre-configured SMTP server, or b) submit the mail message to the local 
mail subsystem (e.g. sendmail, Postfix), and let that subsystem take 
care of delivering it. Whether that subsystem uses MXes for routing its 
mail, or some other method, is entirely up to the how the MTA is 
configured, and not really on-topic for this list.

As a DNS note, however, the "responsible mail addr" you show above is 
probably the RNAME field of an SOA record you got in the Authority 
Section of an NXDOMAIN response. I think you're getting it confused with 
an actual MX target. Using "dig" instead of "nslookup" would probably 
help to clarify this kind of stuff.

                                                                         
                                                      - Kevin



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