[exim] Virtual Users HowTo ???

Hello
I've installed Exim4 on debian sarge squirell webased & Courier for IMAP & POP , it's working fine .. But when i came to configure virtual domains it was OK too (thanks GooGle) but the matter in case i don't like to use system users for my multiple domains .. so i've 2 things to help me with:
1- Virtual users & how they will be authenticated ?
2- Local users already created like this user1@??? user1@??? etc ... i used whole the e-mail as a user name & i even can logon from ssh OK
so it works from squirell to send but not recieve the same from outlook express .. it can be authenticated but when message in the destination reply it doesn't arrive .. some body help me plz !! thanks
A.Sabry