Over time I accumulated enormous Outlook data files. Several “archive” PST’s that I collected from different time periods and different versions of Outlook. And possibly migrating to new computers. In short you end up with large archive PST’s that you have no idea on time span, duplicates etc.
I do try to manually clean conversations on new email daily but sometimes I don’t get time. So a lot of my Outlook email consist of long threads where really only the latest email have the whole 100 previous email content anyhow. So keeping the latest only makes sense.
In short my goal was to end up with several archives containing only one year worth of email and with no duplicates. As well as conversations cleaned sufficiently to just keep latest email in the thread.
First I opened all my various archive PST’s in one Outlook setup. Then I used the archive tool to archive into one very large PST.
Then used a freeware tool to remove duplicates. It does not do Deleted Items though so had to do some moving around for that.
Then used the Outlook clean conversation feature.
Check use custom fields and ran again.
At this point I could use some of the Outlook howtos to clean conversations and remove duplicate items as shown in links below.