Ext. Email with Postfix, Dovecot and MySQL on Ubuntu 10.10

Greetings,

I set up my email services via the 'Host Email with Postfix, Dovecot and MySQL on Ubuntu 10.10 (Maverick)' tutorial. Everything seems to work fine from the linode server itself. However, I cannot access it externally:

• telneting to 173.255.228.27 25 externally times-out, but works fine from the linode server

• Mac mail connects and authenticates to the server fine (see log entries), but doesn't pull any mail down

Dec 31 22:48:17 li238-27 dovecot: pop3-login: Login: user=<do_not_reply@datedecider.com>, method=PLAIN, rip=108.2.122.227, lip=173.255.228.27, TLS
Dec 31 22:48:17 li238-27 dovecot: POP3(DO_NOT_REPLY@datedecider.com): Disconnected: Logged out top=0/0, retr=0/0, del=0/0, size=0</do_not_reply@datedecider.com> 

• I can't send mail to the account from a separate verizon email account. See email rejection:

Your message cannot be delivered to the following recipients:

 Recipient address: DO_NOT_REPLY@pragmatico.datedecider.com
 Reason: Illegal host/domain name found

Reporting-MTA: dns;vms173011.mailsrvcs.net (tcp-daemon)
Arrival-date: Fri, 31 Dec 2010 12:24:55 -0600 (CST)

Original-recipient: rfc822;DO_NOT_REPLY@pragmatico.datedecider.com
Final-recipient: rfc822;DO_NOT_REPLY@pragmatico.datedecider.com
Action: failed
Status: 5.4.4 (Illegal host/domain name found)

• And, I can't set up my domain as an outgoing mail server within Mac mail.

Not sure how to debug the issue. I strongly suspect I messed up my mx record setup.

Thanks in advance for any help debugging my setup.