A Windows tool that clears duplicate emails out of Outlook PST and OST files without touching the original. The unique messages go to a fresh PST you choose.
Point the app at any Outlook data file. The folder tree loads with checkboxes, and each message shows its subject, sender and date, alongside its size.
Tick the folders to scan, then decide what makes two emails a duplicate. You can match on Subject, sender, body text, and more. Cross-folder scanning is on, so Inbox and Sent get compared together.
Keep the first, oldest, or newest message in each group, and set the output folder for the cleaned PST. Turn on the backup file if you want a rollback.
Run the job. It writes a new PST with only the unique emails, plus a CSV log of every group it kept or removed. Open the report in Excel to check the run.
This is the part people worry about most, and the answer is simple. Your source file is left exactly as it was, byte for byte. Duplicates are never deleted in place. The unique messages are written into a separate new PST instead, and the mailbox you started with does not change at all. A wrong guess about what counts as a duplicate costs you nothing. You can try a more strict run whenever you like.
The Clean Up command built into Outlook only removes copies within a single conversation or folder. The real mess is spread wider. The same message sits in Inbox and in Archive, a whole account gets imported on top of another, threads multiply after a repair. One bad re-sync on a busy IMAP mailbox has been enough to push a 22,000-message folder past 33,000. The tool compares across every folder you check, so cross-folder copies finally get caught.
No upload, no web service, no cloud account. Everything happens on your own computer, and the clean copy is saved right there beside the original. For regulated inboxes in law or finance, that on-machine processing is a requirement rather than a bonus, and here it is the default.
Six fields define a duplicate: Subject, sender, message body, recipients, date, and attachment names. Tick the ones that matter. The body is compared as a normalized hash, and RE: and FW: prefixes can be ignored so replies still line up.
For every group of duplicates you choose the survivor. The default keeps whichever copy was found first, and one click switches that to the oldest or the newest. Useful when the tidier, better-filed copy of a thread is the one worth keeping.
Both Outlook file types open the same way, with no Outlook profile or Exchange setup to configure. Browse the full tree, expand every level, and select only what you want scanned.
Narrow the message list with a text filter across the Subject, From, To, and body fields, then apply. It is easy way to preview a slice of the mailbox before committing to a full run.
Each group is logged with its folder, Subject, sender, date, and whether the copy was kept or removed. The file is plain RFC4180 CSV with a UTF-8 marker, so it opens cleanly in Excel.
Switch on the backup and the removed duplicates are saved to a second PST of their own. If you ever want them back, they are one import away.
Cleaning mailboxes after a PST import or an Exchange move, where the same messages routinely land twice and users start complaining about clutter.
A personal archive that grew across years and a couple of email accounts, now heavy and slow to open, full of copies nobody meant to keep.
Handed an inherited mailbox to slim down, such as an ex-colleague's 6 GB archive with three dozen subfolders, before it gets passed on to someone else.
Outlook Duplicate Remover
8 Mb
1.0
04/06/26