[Dovecot] Duplicate message with POP3 and Outlook

[St0rM]

I know that what I am about to say is FOR SURE a problem of Outlook and 
Outlook Express, but since I can't find any know bug like this, and all 
is started when i switched to Dovecot (and I can't exclude is somehow 
related to Dovecot), I would try to ask for help here, maybe someone of 
you already seen that.

I am using dovecot 0.99.13 on a Fedora 1 (0.99.13-1).

The problem I see is that, when a customer using Outlook or Outlook 
Express (many different versions, from Outlook 2003 to Outlook Express 
5, with various patch) via POP, every mail is downloaded TWO times, more 
precisely the first time on the first connection and the second on the 
second, where the mail gets finally deleted.

I tried manually and with many other clients, and pop actually works 
perfectly, and IMAP too. Outlook client have NOT the "Leave mail on 
server" option checked, and nothing similar is around.

I am about to start a sniffing session but it would be problematic for 
privacy questions, and I'm not able to reproduce it so easily, as it 
seems only some of our customers with Outlook have this problem, and the 
(few) trial I've done here seems to go smoothly. So I fear it will be a 
LONG week.

Again, i bet it's an Outlook problem, but... Anyone already seen 
something similar?

Thanks for the help, and for the time. Keep up the good job.