I have postfix installed....everything work in mutt (sending/recieveing) ports are opened for SMTP/POP/IMAP access .....thunderbird or any other external program WILL read mail from server but will NOT send mail (to server then to where it needs to go)...any ideas?

Are you using domain names or ip addresses to connect to the server? If domain names, verify that they resolve correctly.

I know with sending, you can telnet to the server and issue smtp commands directly. This will allow you to send messages to the server mailboxes, not external ones.

Last, some ISPs now block mail relay as a method of controling spam. If you are not on the same network, you may have the ISP blocking the traffic.

As for the linux part, I can't help you with that too much.

Good luck.

Yes, make sure your DNS is setup correctly. You typically need reverse lookup (IP to name) working for email sending to operate correctly. Take a look at dnsreport.com. It will automatically test your DNS setup.

Double-check your SMTP settings. I'm using Thunderbird on Gentoo and can send / receive without any problems through SBC.

pretty sure its the ISP blocking SMTP ports....i guess i coudl use a non-standard port....but the e-mail programs would get pissed...oh well. I currently use the wku mailserver to send mail. works for my buddy (who doesnt pay the server rent )