Merge multiple folders from different Outlook accounts into one

Four accounts in my Outlook, each with its own Projects folder built up over years. I want one consolidated Projects folder I can search and eventually archive as a unit.

What is the clean way to merge without losing anything or creating duplicates?

Merge into a dedicated PST rather than into one of the live accounts. A PST destination keeps the consolidated set independent of any account, which is exactly what you want for later archiving.

1

Create the destination: File, New Items, More Items, Outlook Data File, name it Projects Consolidated. Add a Projects folder inside it.

2

Record the item count of each source folder first: right click, Properties, Show total number of items. Write the four numbers down, their sum is your target.

3

Copy rather than move, one source at a time: open the source folder, Ctrl+A, then right click, Move, Copy to Folder and pick the destination. Copying leaves the originals untouched until you verify.

4

Compare the destination count to your target sum. Matching numbers means the merge is complete and you can delete the source folders at leisure.

Duplicates only exist if the same message lived in multiple accounts to begin with, common when you CCd yourself between them. Sort the merged folder by subject in a list view and identical neighbours stand out for manual pruning, or a dedicated duplicate remover handles thousands at once. Do the dedupe after the count check, never before, otherwise you cannot tell a removed duplicate from a copy that failed.

Four folders copied, destination count hits the sum exactly, 9,412 items. Found about 100 self CC duplicates by subject sort. Clean merge.