it is applicable for all who are using "leave a copy to server" option

 

1. Create one folder in live mailbox. (I named it as Downloaded)

2. Move all mail from your inbox to this folder which are already downloaded to your .pst fille.

 

Now your outlook will stop downloading duplicate entries.

Remember to move your Inbox items to the newly created folder.

 

In future if your local pst is lost or damaged then, in live mailbox move all mails to Inbox and create a new outlook profile; your all mails again will be available in pst.

 

This trick may help...