sending mail with thunderbird
 

I am trying to send email with thunderbird and I am getting errors that I cannot connect to the host. It works with every other email client. The server is mail.domain.com and to send the username is user@domain.com and I need to authenticate when sending mail. It asks me for my password and I put the correct password in. Then it pops up with a message saying that the server may be unavailable or is refusing SMTP connections. Could this be some sort of bug?