Merge PST files without duplicates

Merging and removing duplicates are two steps. A merge keeps every message, so nothing is lost by accident; removing duplicates then writes a clean copy that keeps one of each.

1. Merge the files

Open Merge PST and add two or more PST files. The first one is the base, and the others are added to it. Choose how folders combine:

• Merge matching folders: Inbox goes with Inbox, Sent Items with Sent Items. Best when the files are pieces of the same mailbox.
• Keep each file apart: each file becomes its own top folder. Best when the files belong to different people or accounts.

Preview the merge for free to see how many messages the result will hold, then merge. Every message of every input is compared with the result before you can save it.

If one of the files is an .ost, convert it first with OST to PST, or add it after a PST.

2. Remove the duplicates

Open Remove duplicates with the merged file and choose the rule:

• Same content (recommended): same sender, recipients, subject, sent time, Message-ID, body and attachments, even if the copies were stored differently by different programs.
• Exact copy: every stored property identical, as with copies Outlook made itself.

and where to look:

• In the same folder: a copy filed in another folder is kept.
• Anywhere in the file: the first copy in folder order is kept.

Count the duplicates for free first. Every duplicate is confirmed by a full comparison of the messages, not just a fingerprint, before it is left out of the new file.

Frequently asked

Does this change my original files? No. Both steps write new files; the originals stay as they were.

Why not remove duplicates while merging? Keeping the two steps apart means the merge can be checked message for message, and you see exactly how many duplicates there are before choosing what to drop.

How large can the files be? Each output can be up to 50 GB; very large merges take longer in the browser than in a desktop program.