cyrus-postfix problem

Hi all I've installed cyrus-imap and postfix. I created 2 users are called user1,user2 by using cryadm and tested that whether they can authenticate or not ( it looks fine). the problem is when I try to sent mail from user1 to user2, it fails. I know that this information is too weak to make decision to fix it but I need some suggestions about the reason of this problem. Regards