Can recieve but can't sent

Recently I had to reconfigure my email account - I can now receive emails but can’t send them. When I try to send I get the following error:
"The message could not be sent because the server rejected the sender's email address..."
Verizon support is useless. I’m using Outlook Express with Windows 2K. Any suggestions how to resolve this would be appreciated.

 

Well, quite literally, the SMTP server dislikes your email address in your account setup.

That could be because you don't have your Verizon email address in there, or possibly, aren't using Verizon's SMTP server, OR are using Verizon's SMTP server, and not on Verizon's network.