Proper planning eliminates the possibility of duplication when creating calendar relationships.
When creating calendar relationships in Add2Outlook, the goal is to have one (or more) locations where new or existing appointments are synchronized based on the relationship settings; however, prior to having the automatic Add2Outlook synchronization relationships, users could have MANUALLY copied the items from the public to their private or from their private to their public (source to destination).
Since Add2Outlook does not de-duplicate, if the user copied the items over manually and Add2Outlook synchronized, there could potentially be two of everything, or "duplicates" The next time Add2Outlook synchronized, it would still only have two copies, but one of the duplicates would be tied to the source and the other copy would not. True duplication occurs for only three reasons:
1. Users were invited to a meeting which was created in the public folder and the user also has a public-to-private relationship. This is completely normal and in fact, very handy.
2. When users have been manually copying items from the source prior to implementing Add2Outlook.
3. The Add2Outlook system is configured incorrectly with incorrect memberships or permissions.
Duplication can APPEAR to have happened because items were actually created in both places. After synchronization the two items look very similar, but were actually created separately in both places. This is not duplication. For calendar appointments, there is usually not much duplication; however, contacts and tasks duplication is more common.
In order for Add2Outlook to operate correctly without duplication, the destination folder should be cleaned out manually prior to synchronization or the various source folders should be consolidated to one folder and then de-duplicated there, before relationships are set up. Only after the contents source folder is established and contains only the set of information you want, do you set up an Add2Outlook relationship. Usually the original contents of the destination folder is either deleted or moved (preferably moved to a backup folder).
The destination folder could be cleaned out of any manually copied items after synchronization if the Add2Outlook relationship was set so that if destination items are deleted, the system would recopy the source items, but it is almost always a better idea to do the data de-duplication prior to setting up a relationship in Add2Outlook. If you do de-duplication after synchronization and set to recopy deleted destination items, both duplicate items could be deleted from the destination, and then the right one would come back after synchronization.
Private-to-Public or Public-to-Private: If users are not currently using a public folder, and you are going to make one for these purposes, then there is obviously no duplication in the source or destination. Also, if users are not currently using their private folder, and you want all the items from the public to go to their private, then again there is no duplication.