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To merge PST files with Stellar Merge Mailbox for Outlook, open the program, click Add PST on the Home menu and select the files, choose whether to merge matching folders or join each file under its own root, tick the duplicate, deleted and junk filters you want, then pick a new or existing PST, an Outlook profile, Office 365 or Exchange as the destination. The log report records what was done.
Before you start
Knowing how to merge PST files starts with checking the files. The program reads healthy PSTs only, so open each one in Outlook first; if a file will not open or Outlook reports errors, repair it before going further. Outlook must be installed on the same computer, and the program itself needs 64 bit Windows; the download page has the full requirements.
- Every source PST opens normally in Outlook
- Passwords for protected PST files are at hand
- There is free disk space for the result, roughly the size of all sources combined
- You have a copy of the source files somewhere else
- You know whether you want one combined mailbox (merge) or separate trees (join)
Merge or join: pick first
Merge combines matching folders. Every Inbox becomes one Inbox, every Calendar one Calendar, so the result reads like a single mailbox. Choose it for yearly archives of the same account.
Join creates a root folder for each source file and keeps that file's folder tree underneath. Nothing from different sources is mixed, which is safer when the files belong to different accounts or people. If you are unsure, join: a joined PST can still be tidied by hand later, while a merge is harder to pull apart.
The procedure
- Open the programStart the application. In demo mode everything below works, and the result appears in a preview instead of being saved.
- Add the PST filesOn the Home menu click Add PST, browse to a file in the Open dialog and click Open. Repeat or select several at once. You can also drag files into the window, or use Find PST to search a drive for PST files when you do not know where they are.
- Enter passwordsFor a password protected PST, type its password when asked. Protected and unprotected files can be combined in the same run.
- Choose merge or joinPick the saving mode: merge to combine matching folders, or join to keep one folder tree per source. To combine only some folders, such as Contacts or Calendar, select just those.
- Set the filtersTick the duplicate option and choose default or advanced criteria. Tick Exclude Deleted Folder and Exclude Junk Folder to leave those out of the result.
- Choose the destinationSelect a new PST, an existing PST, an Outlook profile, Office 365 or an Exchange server, then browse to the location. For Exchange enter the login, the mailbox email address and the server name.
- Run and check the logStart the job. Time depends on the size of the files. When it ends, open the log report to see the mode, destination, start and end time, source files and folders, and save it if you need a record.
How the duplicate filter decides
Two items count as duplicates when they match on the fields in the criteria you choose. The default set suits most merges of the same account across several archives. Use the advanced set when you want stricter matching, for example adding attachments and internet header so that forwarded copies with different attachments are kept.
- Subject
- Sender email and sender name
- Recipient name
- Text of the message
- Internet header
- Attachments
- Date and time sent
Which destination to choose
| Destination | When to use it |
|---|---|
| New PST | Default choice; leaves every existing file untouched |
| Existing PST | Adding older archives into the file you already use |
| Outlook profile | Putting the result straight into the mailbox Outlook opens |
| Office 365 | Moving consolidated mail into a cloud mailbox |
| Exchange server | On premises mailboxes; needs login, mailbox address and server name |
If something goes wrong
A file that fails to load is usually damaged. The vendor states that corrupt PSTs cannot be merged; repair the file first, then add it again. The Toolkit edition includes a repair module, as the edition comparison shows.
If the merged file is very large, consider joining yearly archives into two or three files instead of one. If you only have two small files and no duplicates, Outlook's own wizard may be enough; the comparison with Outlook Import/Export shows where each method fits. The review lists the remaining limits.
Run the merge in the demo first
The preview shows the result before you buy a key.
Frequently asked questions
How do I merge multiple PST files into one?
Add all the files with Add PST on the Home menu, choose merge, set the duplicate filter, and save to a new PST. Matching folders from every source are combined into one folder tree.
Can I merge PST files without duplicates?
Yes. Turn on duplicate removal and pick default or advanced criteria. Items are compared on fields such as subject, sender, recipient, text, header, attachments and sending time.
Can I merge only contacts or calendars?
Yes. Select only the folders you want, such as Contacts or Calendar, and the rest of each PST is left out of the result.
Will merging change my original PST files?
The vendor says the originals are not modified unless you choose an existing PST as the destination, in which case that one file receives the new items. Keep backups until you have checked the result.
How long does a merge take?
The vendor gives no figures and says the time depends on the size of the files. Many small files or one very large archive will take longer than two small ones.
Why does a PST fail to load?
The most common reason is damage to the file; corrupt PSTs cannot be merged. Repair it with a PST repair tool, then add it again.