I'm currently using Windows SharePoint Service 3.0 (WSS) with Outlook 2007 and I have numbers of different Discussion Groups (DGs) under different sites on SharePoint.

All of my users use Outlook 2007 to read/post new items on Discussion Groups, but 3 of them creates duplicate posts (for the same item) on DGs.

When there is a new post on a DG and one of the problematic user posts a reply, I'll have multiple posts (with the same content from the same user) in couple of hours. Like 50 posts in 2 days...

I monitor the users communication from Outlook to SharePoint, this happens when
1. They open and login to Outlook and SharePoint
2. They push Send/Receive on Outlook (which updates all the folders including SharePoint lists)
3. They try to access to a DG on Outlook

Ive checked their Outlook rules and they dont have any rule related to SharePoint DGs.

Most of my users are subscribed to each DGs to get email alert for each update, with each duplicate post they get an email alert. It turns to spamming the mailboxes with hundreds of emails in the short period of time.

Any ideas to what might be causing the duplicate posts?