UNIX for Dummies Questions & Answers

Hello fellow unix dudes, I have a question on DNS.

Basically the error is my domain.com server can not send email to my
mail.domain.com server.

I have a virtual server with one IP say 192.10.11.12 and a mail server with
iP 172.4.5.6

When the virutal server on ip 192.10.11.12 was setup, it was setup with DNS with the following named.conf

Code:

zone "192.10.11.in-addr.arpa" {
        type master;
        file "192.10.11.in-addr.arpa";
        allow-transfer {
                common-allow-transfer;
        };
};
zone "domain.com" {
        type master;
        file "domain.com";
        allow-transfer {
                192.10.11.12;
                common-allow-transfer;
        };
};
acl common-allow-transfer {
        none;
};

My question is how do I setup the virtual server on 192.10.11.12
(domain.com) to send email to 172.4.5.6 (mail.domain.com)???

I can email gmail fine and I can even telnet to port 25 on mail.domain.com.

Just seems to be a DNS issue when trying to send an email from domian.com to user@domain.com not seeing the mail.domain.com server.

Any insight would be appreciated, thanks.