How to configure Thunderbird email client?

I am having difficulty configuring my Thunderbird email client running on a Windows 10 PC to send email.  This is how my Outgoing Server (SMTP) is configured:

Server Name:  outbound.att.net

Port:  465

Connection Security:  SSL/TLS

Authentication Method:  Normal Password

Username:  my att username with the @att.net portion not included

When I try to send a message there is a long pause and then I'm asked for my password.  I type in my password and I'm told "Login to server outbound.att.net failed" and I'm asked to retry my password.

The status message states that I'm connected to att.net but my password isn't accepted.

Any idea what I'm doing wrong?

Thanks!