Exactly what happens when you try to send an email? Are you getting any error message? Can you send normally using only a browser and the webmail interface?
in the iphone app it just sits in the outbox, no error message
in the MailBird appilcation, I get an error, which I am contact with the Mailbird team about, but it is more likely on comcast's end since all of my other addresses in both applications work.