Ubuntu :: Thunderbird - Can Receive But Not Send Email

I have a desktop that has been running Ubuntu for years. Finally I convinced my wife to get rid of windows XP and move to Lucid. I did a clean install of Lucid on her system writing over windows. After the install I installed Thunderbird using Synaptic Version 3.0.6 was installed on her system. On my desktop I am also running Thunderbird 3.0.6 We have several domains and mail servers on those domains.

They all use SMTP First, I installed the ISP email and that works perfectly. She can send and receive using our ISP's mail server. I then set up an email account in Thunderbird using the SMTP email server form one of our domains. She used to be able to send and receive from for one of our domains. She can receive email from that email server, but can not send (I can send and receive from the same domain using Thunderbird) Her SMTP and mine are set up identically:

Server Name: mail.[domain]
Port: 50
Username: [user]@[domain]
Secure Authentication: No
Connection Security: No

She is able to receive email but when she tries to send. the connection in Thunderbird either times out. or gives a password error. The password is correct, because we can use Firefox, and go to the pop and log in.Also, she can receive email direct on her computer and has to log in using her password. So I opened Terminal and tested using:

telnet mail.[domain] 50

I got

Trying [IP address]
Connected to mail.[domain]
Escape character is '^']'.
220 mail.[domain]

This leads me to believe something in Ubuntu is blocking her system from using Thunderbird to send emails through the email server. I've been at this for several days now. I did try totally un-installing Thunderbird using Synaptic. Then manually deleting the .Thunderbird file. Then doing a fresh install of Thunderbird using Synaptic. Still get the same results I am thinking that maybe App Armor is stopping this? Or perhaps some other security issue in Ubuntu like Linux Security Module? Otherwise the installation went flawlessly. We even got Skype working on the first try! Printers installed correctly and perfectly too.