Thunderbird Problems

Alright, I recieved 50 e-mail accounts from Brinkster when I got my web-hosting. I want to set-up one of them, ectheo@ectheo.com, with Thunderbird.

I got everything set-up, BUT, Brinkster requires that it has a Mail Send Authentication. It has step-by-step instructions for Outlook, OE, and Macintosh, but nothing else. I contacted customer support, and they said that yes, I can use Thunderbird, but that it needs to have mail send verification.

Anyone know where this is located in Thunderbird?