Why should You Split a Large PST File?
Microsoft sets the default PST size limit at 50 GB for the Unicode format, and the old ANSI format stops at 2 GB. Outlook shows a message that the data file has reached its maximum size when you hit the limit.
Large files open slowly and search slowly, too. Splitting spreads your mail across several smaller files.
| Method | Splits by | Needs Outlook |
|---|---|---|
| Outlook archive | Date | Yes |
| New PST and manual move | Folder or date range | Yes |
| Split software | Date, size, year, folder or category | No |
What should You do Before You Split?
- Copy the PST file to a safe folder.
- Empty the Deleted Items folder.
- Select File, Account Settings, Data Files and your file, then Settings and Compact Now.
Microsoft explains Compact Now and the search messagesize:>5 mb to find large messages. Outlook compacts a file on its own only when more than 20 percent of it is unused space.
How does Outlook Divide a File?
Method #1: Outlook Archive (Free With Outlook)
- Select File, then Cleanup Tools and Archive.
- Select Archive this folder and all subfolders and choose the account or folder.
- Set the Archive items older than date.
- Select Browse and name the new PST file.
- Select OK.
Outlook moves older items into the new file, so the original shrinks.
Method #2: New PST File and Manual Move (Free With Outlook)
- Select File, Account Settings and the Data Files tab.
- Select Add and create a new PST file, for example Archive_2020_and_older.pst.
- Drag older folders or date ranges into the new file.
- Compact the original file again.
Our guide to split a PST file by date shows more detail on date splits.
What Splits Files Without Outlook?
Method #3: PST Splitter Software (Paid After Demo)
The PST Splitter divides a file by date, size, year, folder or category, and it works with no Outlook installed.
- Install the software and add the PST file.
- Choose a destination folder and select Next.
- Select the split option, like Split by date, and set the value.
- Check the summary and select Next to start.
The trial splits a limited number of items, so test the result before you buy. Open the new files in Outlook and compare the folder counts with the original.
Frequently Asked Questions
How Big can a PST File be?
The Unicode format has a 50 GB default limit, and the old ANSI format stops at 2 GB.
Does Outlook Divide It by Itself?
No. Outlook archive moves older items into a new PST file, which splits the original by date.
Does Deleting Mail Shrink a PST File?
Not at once. Outlook compacts the file when over 20 percent is unused space, or you can select Compact Now.
Can You Divide It Without Outlook?
Yes, with split software. Windows has no built in tool.
Will the Original Disappear?
No. Retain the original until you check the new files.
How do You Find Large Messages in Outlook?
Type messagesize:>5 mb in the Outlook search box. Microsoft lists this tip on its support page.
What Size should the New Files have?
Hold every file well below 50 GB. Smaller files open faster and break less frequently.
Author's Verdict
Compact first and split by date with Outlook archive when you have Outlook.
Use split software for huge files or a computer with no Outlook, and compare counts after the split.
Key Takeaways
- Unicode PST files stop at 50 GB by default.
- Archive splits a file by date.
- Always work on a copy.
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