Duplicate mail items in INBOX

Exchange : 2000 SP4
Outlook : 2002
Working off- and online causes my Inbox being populated with a lot of duplicate messages
I’ve setup a POP account to be able to read my mail offline (I do not have the possibility to setup a VPN connection) and an

Exchange account for online usage. The problem often occurs after I’ve been online the previous day and then work offline

and retrieve my mail via the POP account. Also the other way around causes problems but not always.
The Send/Receive are adapted accordingly (online and offline settings)

What am I doing wrong or did I forget to configure ?

I’ve seen some messages with the same problem but no answers to solve this.