Outlook 2010 and later limit a PST or OST file to 50 GB by default. Older Unicode files stop at 20 GB. Reduce the file with Archive or Move Folder. Raise the limit in the registry after a backup. Microsoft advises against limits above its table values because performance can drop.
Outlook shows that a PST file has reached its maximum size and stops moving items. You can reduce the file or raise the limit.
Facts follow Microsoft Learn pages on PST and OST size limits and configuring data file limits.
What are the PST and OST Size Limits?
| Version | Default limit |
|---|---|
| Outlook 2010 and later | 50 GB (51,200 MB) |
| Outlook 2007 and 2003 | 20 GB (20,480 MB) |
| Warn value 2010 and later | 47.5 GB (48,640 MB) |
Microsoft states Outlook 2007 or 2003 cannot open a Unicode PST file above 20 GB that Outlook 2010 or later created.
What Happens at the Limit?
- Compaction. Outlook starts compaction to reduce the file.
- Restricted actions. You cannot send messages when Sent Items sits in that file and you cannot copy or move items inside it.
- Auto-Archive. Auto-Archive fails for archive PST files.
- Delete. You can still delete or archive items when the file is the default delivery location.
How do You Reduce the File Size?
- Open File then Info and select Cleanup Tools then Archive.
- Move older items to another PST file.
- Select Move Folder to move single folders to another PST when Archive is not enough.
How do You Raise the Limit in the Registry?
Backup the registry first because wrong edits can cause serious problems. Open regedit and go to the Outlook PST policy key for your version. Use 16.0 for Outlook 2016 and later.
- Go to
HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\Outlook\PSTand create the PST key when it is missing. - Create a DWORD (32-bit) Value named
MaxLargeFileSize. - Open the value, choose Decimal and enter the size in MB.
- Repeat for
WarnLargeFileSize.
Microsoft advises a gap of at least 5 percent between the two values. Steps follow the Microsoft page and are untested. Related reading: why an Outlook data file does not compact and how to reduce Outlook attachment size.
Frequently Asked Questions
What is the Default PST Size Limit?
Microsoft states 50 GB for Outlook 2010 and later.
How do I Make a PST File Smaller?
Use Archive under Cleanup Tools or move folders to another PST.
Can I Raise the PST Limit?
Yes. Edit MaxLargeFileSize in the registry. Microsoft advises against values above its table.
Does Outlook Warn Before the Limit?
No. Microsoft states these entries do not make Outlook warn you.
Key Takeaways
- Outlook 2010 and later default to a 50 GB PST and OST limit.
- Outlook blocks moves and sends at the warn limit.
- Archive and Move Folder reduce the file.
- MaxLargeFileSize raises the limit.
- Backup the registry before any edit.
Sources and References
Facts follow Microsoft Learn.
- File size limits of .pst and .ost files in Outlook 2010 and 2013 (Microsoft Learn) learn.microsoft.com
- Configure the size limit of Outlook data files (Microsoft Learn) learn.microsoft.com