An A record is an MX record and is a missing MX....

Fri Apr 4 22:33:40 UTC 2003

There is one other situation where you need an MX record.  If your domain
is foo.com and the A record for foo.com is _NOT_ the machine that accepts
mail for foo.com, you need an MX record pointing to the correct machine.
Often this will be mail.foo.com or smtp.foo.com.

Owen

--On Friday, April 4, 2003 10:13 AM +0800 Indra PRAMANA 
<indra at indra.webvis.net> wrote:

>
> At 03:58 PM 4/3/2003 -0600, Gerardo Gregory wrote:
>> Since then I have learned that some MTA's will look for an A record if
>> it  cannot find an MX record and use the A record instead.
>
> This is always the case. MX records are only required if you want to have
> more than one mail exchange servers to serve your domain, e.g. if you
> want to have a secondary mail server as a relay if the primary server
> goes down.
>
> If you only have one mail exchange server to serve your domain, you don't
> need MX records. An A record pointing to your mail server is sufficient.
>
> -ip-
>