Can't send mail

[Mike1138]

I am able to receive email but I am not able to send. My email server requires me to use my entire email address to log in (mydomain@domain.com). When I get the message to enter my password when trying to send mail it says enter password for domain on the mail server instead of mydomain@domain.com. I think this is the problem, but I am unable to find a way to change this setting. Any suggestions?