My Zimbra server is setup and running great except for the fact that I can no longer send to some external addresses. For example I can send to my server hosted on supremecluster, but I can't send to gmail.com, yahoo.com, or msn.com. I've searched the web and the forums for some type of solution, but nothing is working. I have attempting setting up CNAME and PTR records in DNS as well as SPF records, and modifying the firewall but nothing changes the outcome. Below are the logs I am receiving; any ideas?

------------ Logs ------------
Aug 14 11:45:41 servername postfix/smtp[17423]: connect to gmail.com[74.125.127.83]: Connection timed out (port 25)
Aug 14 11:45:41 servername postfix/smtp[17419]: connect to gmail.com[74.125.79.83]: Connection timed out (port 25)
Aug 14 11:45:41 servername postfix/smtp[17422]: connect to gmail.com[209.85.225.83]: Connection timed out (port 25)
Aug 14 11:45:41 servername postfix/smtp[17424]: connect to gmail.com[209.85.225.83]: Connection timed out (port 25)
Aug 14 11:45:41 servername postfix/smtp[17425]: connect to gmail.com[74.125.79.83]: Connection timed out (port 25)
Aug 14 11:45:41 servername postfix/smtp[17419]: 1B35667CA4: to=, relay=none, delay=246750, delays=246660/0.02/90/0, dsn=4.4.1, status=deferred (connect to gmail.com[74.125.79.83]: Connection timed out)
Aug 14 11:45:41 servername postfix/smtp[17423]: D740967CA5: to=, relay=none, delay=240224, delays=240133/0.03/90/0, dsn=4.4.1, status=deferred (connect to gmail.com[74.125.127.83]: Connection timed out)
Aug 14 11:45:41 servername postfix/smtp[17422]: 1757967CD7: to=, relay=none, delay=3397, delays=3307/0.02/90/0, dsn=4.4.1, status=deferred (connect to gmail.com[209.85.225.83]: Connection timed out)
Aug 14 11:45:41 servername postfix/smtp[17424]: B6C9967CB3: to=, relay=none, delay=141523, delays=141432/0.03/90/0, dsn=4.4.1, status=deferred (connect to gmail.com[209.85.225.83]: Connection timed out)
Aug 14 11:45:41 servername postfix/smtp[17425]: 8197367CD8: to=, relay=none, delay=3387, delays=3297/0.04/90/0, dsn=4.4.1, status=deferred (connect to gmail.com[74.125.79.83]: Connection timed out)
Aug 14 11:45:41 servername postfix/qmgr[17766]: warning: connect to transport retry: Connection refused
Aug 14 11:45:41 servername postfix/qmgr[17766]: 63C9367CC0: to=, relay=none, delay=78572, delays=78482/90/0/0, dsn=4.3.0, status=deferred (mail transport unavailable)
------------ Logs ------------