Dovecot problem ?!

[Franco <primo ischianet com>]

Hi, i have installed a fresh copy of FC4, i use it as web and mail 
server, i have a problem with pop3, i use dovecot, my customers try
to download e-mail but the server when have mail on the server and
the client delete e-mail without download it. The client have
configured correctly.
Can someone help me? Can someone tell me how can set detailed log
of dovecot?
Best regards.