What is the Size Limit for a PST File?
Outlook stores mail in a PST file. The file stops growing at a size limit. The limit depends on the format and the Outlook version.
| Format | Outlook version | Default limit |
|---|---|---|
| ANSI | Any version | 2 GB hard limit |
| Unicode | Outlook 2003 and 2007 | 20 GB |
| Unicode | Outlook 2010, 2013 and 2016 | 50 GB |
These values come from the Microsoft page on Outlook data file size limits. The Microsoft table stops at Outlook 2016. Third party guides report the same 50 GB default for Outlook 2019, 2021 and Microsoft 365.
Why is Your PST File Too Big for Outlook?
An oversized PST file shows up in a few ways. Outlook says the file reached its maximum size. Another sign is a file that fails to open, copy or import.
- Outlook 2007 and 2003 cannot open a Unicode PST file above 20 GB. Microsoft states this in its PST and OST size limit article.
- A FAT32 drive stores no file above 4 GB. Move the file to an NTFS drive.
- The Microsoft 365 Import service asks for PST files of 20 GB or less and ignores items above 150 MB.
- A PST file near the size limit slows Outlook and raises the damage risk.
Heads Up. Create a copy of the PST file before you try any method below.
How do You Reduce a PST File With Compact Now?
Method #1: Compact Now (Free)
Who it suits. Users whose PST file holds deleted items. Extra application. None.
- Delete the mail you no longer need.
- Open the Deleted Items folder and select Empty Folder. Deleted mail frees no space until you do this.
- Right click the PST file in the folder pane and select Data File Properties.
- Select Advanced and then Compact Now.
Compact Now reclaims the unused space inside the PST file. A large file can need several hours, so let the process finish.
The method shrinks a heavily used file only a little. Use Method #2 or Method #3 when the file remains near the size limit.
How do You Move Mail Into a New PST File?
Method #2: New PST File (Free)
Who it suits. Users who can still open the file in Outlook. Extra application. None.
- Create a new Outlook Data File and open it. The new file appears in the folder pane.
- Create the folders you need in the new file.
- Drag older mail from the large file into the new file.
- Use Compact Now on the large file after the move.
Microsoft recommends this approach in its size limit article. The article advises that you break up a big PST file and move mail into another PST file when archiving does not reduce the size.
How do You Split a PST File Outlook Cannot Open?
Method #3: SysTools PST Splitter (Paid)
Who it suits. Owners of a PST file too large to open or move by hand. Extra application. Windows software.
The SysTools PST Splitter divides a file by size, date, year, folder, email ID, category, subject or sender. The vendor page lists ANSI and Unicode PST files and Outlook 2000 to 2021.
- Start the software and select Add File.
- Choose the destination folder for the smaller files.
- Select the split criteria and enter the split value.
- Review the summary and select Next to start.
The vendor page states that the software works without Outlook. The free demo splits the first 50 items.
Read the guide to split a large PST file for the full walkthrough. Read the guide to split a PST file by date when you want one file per year.
Should You Raise the PST Size Limit in the Registry?
Method #4: Registry Limit (Free, Not Recommended)
Who it suits. Admins who accept the performance cost. Extra application. Registry Editor.
The Microsoft page names two Unicode values. MaxLargeFileSize sets the limit in MB and WarnLargeFileSize sets the warning level.
Microsoft states that you can set a Unicode limit above the default, but the page does not recommend it because performance can drop. The ANSI limit remains 2 GB. Outlook ignores a larger ANSI value.
Reduce the file with Method #1, #2 or #3 first. Raise the size limit only for a short time while you move data out. Use Compact Now when the move ends.
Where Else do You Go From Here?
- Repair a damaged file with the guide to repair a corrupt PST file.
- Fix the open error with the guide for a PST file with an open error.
- Read the list of errors in a PST file when Outlook reports damage.
- Read the guide to break up big PST files in Outlook 2007 for an older version.
Frequently Asked Questions
What is the PST File Size Limit in Outlook 2016?
Microsoft lists a default Unicode limit of 50 GB for Outlook 2010, 2013 and 2016.
What is the Size Limit for an ANSI PST File?
The limit is 2 GB. Outlook ignores a larger value to prevent damage.
Does Compact Now Shrink a PST File?
Yes. Compact Now reclaims unused space, but a heavily used file shrinks only a little.
Why does the PST File Remain Large After You Delete Mail?
Deleted mail moves to the Deleted Items folder. Empty that folder and then use Compact Now.
Can You Raise the PST Size Limit?
Yes, with the registry values. Microsoft does not recommend it because performance can drop.
What Size does the Microsoft 365 Import Service Accept?
Microsoft asks for PST files of 20 GB or less. Items above 150 MB are ignored.
Can You Open a PST File Above 20 GB in Outlook 2007?
No. Microsoft states that Outlook 2007 and 2003 cannot open a Unicode PST file above 20 GB.
Author's Verdict
Use Compact Now first when the PST file holds deleted items. Move mail into a new PST file when the size remains high.
Split the PST file when Outlook cannot open it or when you must remain under 20 GB for an import.
Key Takeaways
- The default Unicode PST limit is 50 GB from Outlook 2010 and 20 GB before that.
- Compact Now frees unused space only.
- Splitting is the safe fix for a file Outlook cannot open.
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