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Stellar Merge Mailbox for Outlook earns 7.4 out of 10 in this review. It does what Outlook's own import wizard cannot: it takes many PST files in one run, joins them with separate folder trees, filters duplicates on eight fields and logs the job. Against it are a one year licence for a tool many people use once, no handling of corrupt files in Standard, and a 64 bit Windows only requirement.
Verdict
Buy Standard if you have several PST files, especially large archives or password protected ones, and want them combined in one pass without duplicates. Skip it if you have two healthy files and an evening to spare, because Outlook's own wizard handles that for free. The score reflects the documented features and price, not lab measurements.
- Merge or join many PST files in one run
- Duplicate filter on eight fields with default and advanced criteria
- Saves to new or existing PST, Outlook profile, Office 365 or Exchange
- One year licence for a job that is often one off
- Corrupt files must be repaired first
Run the demo first: it previews the full result before you buy.
What it is and who it is for
This review covers Stellar Merge Mailbox for Outlook 8.0.0.3, released in December 2024. It is a desktop program for 64 bit Windows that reads several Outlook PST files and writes their contents into one destination. The source files stay untouched, which matters if the PSTs are your only copy of old mail.
The typical user has one PST per retired account, a run of AutoArchive files, or backups copied from earlier computers. Outlook can open all of them side by side, but every extra file is another folder tree in the navigation pane and another file to back up. Combining them leaves one file to open, search and copy. If you want to see the procedure before reading the rest, the merge walkthrough lists every step.
Merge and join
Merge combines matching folders: every source Inbox goes into a single Inbox, every Contacts folder into one Contacts folder, and so on. It suits people who want one continuous mailbox. Join is the cautious option: it creates a root folder per source file inside the final PST and keeps each original hierarchy underneath, so nothing from two different accounts is mixed together.
Both modes can be restricted to chosen folders. The vendor's own FAQ gives the example of merging only Contacts from several files, and the same applies to calendars, journals, tasks and to do items. Archive files and PSTs from different Outlook profiles are accepted.
Duplicates, deleted items and junk
Duplicate removal is the feature that separates the program from Outlook's wizard. Items are compared on subject, sender email, text, sender name, recipient name, internet header, attachments and the date and time sent. Default criteria cover the usual case; advanced criteria let you choose which fields must match. Two checkboxes, Exclude Deleted Folder and Exclude Junk Folder, leave those folders out of the result.
When the run ends the program writes a log with the mode, destination, start and end time, source files and folder names. That is useful when you merge on behalf of someone else and need a record of what went in.
Where the result goes
The manual lists five saving targets: a new PST, an existing PST, an Outlook profile, Office 365 and an Exchange server. For Exchange you supply the login, the mailbox email address and the server name. Saving into an existing PST means you can add last year's archive to this year's file without creating a third one.
If your mail is not in PST files at all, for example a Gmail or Thunderbird account, Standard is the wrong edition. Technician reads those sources; the edition and price breakdown lists what each one adds.
Limits and gaps
Corrupt files are out of scope: the vendor says plainly that damaged PSTs cannot be merged and must be repaired first. Outlook has to be installed on the same computer. The data sheet lists 64 bit Windows 11, 10, 8.1, 8 and Server 2012, while another paragraph on the same page still mentions Windows 7, so treat Windows 7 as unconfirmed.
Every licence on the buy page is described as one year, and the page does not say whether it renews automatically. For a tool many people need once, that is the weakest point; the refund terms are worth reading before you pay. The vendor also publishes no installer size and no speed figures, only that time depends on file size. The free route is compared in this side by side with Outlook's wizard, and paid rivals are on the alternatives page.
Pros and cons
Pros
- Many PST files per run, of any size according to the vendor
- Join mode keeps each source in its own folder tree
- Duplicate filter on eight fields, with default and advanced criteria
- Excludes deleted and junk folders with one checkbox each
- Five saving targets including Office 365 and Exchange
- Demo previews the complete result before purchase
Cons
- Every listed licence runs for one year
- Corrupt PST files must be repaired separately
- Needs Outlook installed and 64 bit Windows
- Installer size and renewal terms are not published
- Non PST sources need the $129 Technician edition
Check the preview, then decide
The download page has the requirements, the demo limit and the install steps.
Frequently asked questions
Is Stellar Merge Mailbox for Outlook worth it?
It is worth $39.99 if you have several PST files, large archives or password protected files and want duplicates removed in one pass. For two small healthy files, Outlook's free Import/Export wizard can do the job with more manual work.
Is it safe to use on my only copy of old mail?
The vendor states that the original PST files are not modified; the result is written to a separate destination. Keep a copy of the sources anyway until you have checked the merged file in Outlook.
What is the difference between merge and join?
Merge combines the contents of matching folders, so all Inbox folders become one Inbox. Join creates a separate root folder for each source file inside the final PST and keeps every original folder tree intact.
Does it remove duplicates?
Yes. It compares items on subject, sender email, text, sender name, recipient name, internet header, attachments and sending date and time, with default and advanced criteria to choose from.
Can it merge Gmail or Thunderbird mail?
Not in Standard, which handles PST files. The Technician edition merges Microsoft 365, Gmail, Yahoo and Outlook.com accounts, DBX and NSF files, and identity folders from more than 20 mail clients.