Sending /Receiving Email Help!

I'm having this problem.

I'm on CentOS 5.2 Postfix Dovecote IMAP/POP3

When sending email through gmail, I get this error:

The mail system

<ashier-xxx.xxx@localdomain.localdomain> (expanded from <ashier@xxx.xxx>): Host or domain name not found. Name service error for name=localdomain.localdomain type=A: Host not found

Final-Recipient: rfc822; ashier-xxx.xxx@localdomain.localdomain Original-Recipient: rfc822;ashier@xxx.xxx Action: failed Status: 5.4.4 Diagnostic-Code: X-Postfix; Host or domain name not found. Name service error for name=localdomain.localdomain type=A: Host not found

I have installed squirrelmail and I can send email through that, but I can't receive any emails.

What should I do? Please help...