[CentOS] Mail delivery failing with 450

Sat Mar 7 13:01:58 UTC 2009
Joebstl Thomas <mlistjoebstl at phorus.at>

Hi James,

MX-records must point to A-records and not to IP adresses.
A "dig -t AXFR obrien-pifer.com @ns1.obrien-pifer.com | grep MX" returns:
mail.obrien-pifer.com.  38400   IN      MX      1

Whereas you list "mail.obrien-pifer.com.    IN    MX    1" 
in your config.

So your setup is invalid because:
- you're pointing your one and only MX record directly to an IP
- since it is interpreted as host and missing a "." at the end it's 
expanded to "" which doesnt exist
- it's a MX record for mail.obrien-pifer.com and not obrien-pifer.com

Your whole definition of the MX record looks goofy to me, dont want to 
sound like an a.. but you better (re)read some tutorials on setting up DNS.
I really wonder if you receive the reply at all.