Main account mail relaying problem

Hi,

I have a problem with sending emails from the main account of each user. After creating a new user, cpanel automaticly creates and receives mail for username@domain.name. It is called the main account.

I can download email using pop3 and cpanel's user/pass combination.
The problem occures when I try to use SMTP authentication. The same user/pass combination doesn't work. Exim logs show information that user authentication has failed.

I found a workaround, which is to create another mail account with the same username and use a full email adres as the username for pop3 and smtp.

It would be a lot less complicated if my clients could use the same username/password as in cpanel to download and send their emails. Is there any way to make it work?
Looking forward to a fast reply..

Cheers,
Remik