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For two or three healthy PST files, Outlook's Import/Export wizard does the job for free: you import each file into one mailbox or data file and tell it not to import duplicates. Stellar Merge Mailbox for Outlook is worth paying for when you have many files, want each source kept in its own folder tree, need finer duplicate matching or want to send the result straight to Office 365 or Exchange with a log.
What Outlook already does
Comparing Stellar Merge Mailbox vs Outlook import starts with the free option. In classic Outlook for Windows, File, Open & Export, Import/Export starts a wizard. Choose Import from another program or file, then Outlook Data File (.pst), browse to the source, and pick how duplicates are handled: replace them, allow them, or do not import them. You then choose which folder to import and whether to import into the current folder or into the same folder in another mailbox or data file.
That is a merge in all but name. To combine five files you repeat it five times, into the same target PST. It is slow but costs nothing and needs no extra software, which is why it should be your first attempt with a small number of files.
Side by side
| Outlook Import/Export | Merge tool (Standard) | |
|---|---|---|
| Price | Free with Outlook | $39.99 for a 1 year licence |
| Files per run | One | Many, any size according to the vendor |
| Combine matching folders | Yes, by importing into the same folders | Yes, merge mode |
| Keep each source separate | Only by importing into a new subfolder by hand | Yes, join mode creates a root per file |
| Duplicate handling | Replace, allow, or do not import | Default or advanced criteria on eight fields |
| Skip deleted and junk | Untick folders by hand | One checkbox each |
| Password protected PST | Asks for the password | Asks for the password |
| Destinations | Mailbox or data file open in the profile | New or existing PST, profile, Office 365, Exchange |
| Log of the run | No | Yes |
| Corrupt PST | Not supported | Not supported |
| Needs Outlook | It is Outlook | Yes, installed on the same PC |
When the free wizard is enough
- Two or three files, all healthy
- Same account across several archives, so merging folders is what you want
- You are fine with the wizard's simple duplicate switch
- The target is a PST or mailbox already open in Outlook
- You do not need a record of what was imported
When the paid tool earns its price
Volume is the main reason. Ten yearly archives mean ten wizard runs with ten chances to pick the wrong folder; the merge tool takes them all in one job. Join mode is the second reason: it keeps each account's tree under its own root without you creating folders first.
The third is duplicates. The wizard's switch decides on its own what counts as a copy. The tool lets you choose the fields, including attachments and internet header, which matters when the same mail exists in several archives with small differences. Office 365 and Exchange as direct targets, and the log, mostly matter to people doing this for someone else. The step by step merge shows how these options appear in the program, and the full review weighs them against the one year licence.
What neither can do
Neither route repairs a damaged PST. Outlook ships an Inbox Repair Tool for that; the paid route is a dedicated repair program, which the vendor bundles in its Toolkit edition. Neither turns Gmail or Thunderbird mail into a PST either; for that you need the Technician edition or another converter, some of which appear on the alternatives page.
Have more than a handful of files?
Try the demo on all of them at once and compare the preview with what the wizard gave you.
Frequently asked questions
Can I merge PST files without any extra software?
Yes. Classic Outlook's Import/Export wizard imports one PST into another mailbox or data file. Repeat it for each source file and choose not to import duplicates.
Does Outlook's import remove duplicates?
It offers three choices: replace duplicates, allow them, or do not import them. It does not let you choose which fields define a duplicate, which the paid tool does.
Is the paid tool faster than the wizard?
The vendor publishes no speed figures. The practical saving is that one run handles many files, while the wizard needs one run per file.
Can the wizard keep each PST in its own folder?
Only if you create a subfolder for each source by hand and import into it. The merge tool's join mode does this automatically.
Does either method work in new Outlook for Windows?
This comparison covers classic Outlook, where the Import/Export wizard lives. The merge tool also needs a desktop Outlook installation on the same computer.