Unfortunately for the case of a Unite email account penguin3107 is mistaken.
Kromega: I have a recollection of setting Unite up with an SMTP server that needed authentication. That was a while ago and I only did it for testing. I think the authentication is on the advanced page, in the same place you set the port and SSL. Or I made the whole thing up in a dream
I'm out of the office until Thursday, but I will have a look at it then if no one else has posted a definitive answer by then.