If your Outlook application is returning errors when sending or receiving emails, it may be because the Outlook PST file is oversized and has reached its maximum size limit. Outlook limits the PST file size; once the limit is reached, the file stops accepting new data until you raise the limit or free up space. In this guide, we will cover the default file size limits on different Outlook versions, how to increase Outlook PST file size limit using the Windows registry, and methods for safer alternatives if you don’t want to touch the registry at all.
Default Outlook PST File Size Limits
The Outlook PST file size depends on the version of MS Outlook you are using and the format of the PST file used(ANSI or UNICODE).
| Outlook Version | Default Maximum PST Size |
| Outlook 2002 and earlier (ANSI format) | 2 GB — cannot be increased |
| Outlook 2003–2007 (Unicode format) 2 | 20 GB, expandable up to 50 GB |
| Outlook 2010–2021 (Unicode format) | 50 GB |
| Microsoft 365 (Unicode format) | 50 GB |
What Controls the Outlook PST Size Limit
There are four important registry values for the Outlook PST file size.
- MaxFileSize – the hard ceiling for ANSI-format PST files, in bytes
- WarnFileSize – the warning threshold for ANSI-format files, in bytes
- MaxLargeFileSize – the hard ceiling for Unicode-format PST/OST files, in megabytes
- WarnLargeFileSize – the warning threshold for Unicode-format files, in megabytes
How to Increase the PST File Size Limit via Registry Editor
Before you start to edit the registry, back up your PST file first. Editing the registry can sometimes corrupt the PST file if not done correctly.
- Close Microsoft Outlook.
- Press Windows key + R
- Type regedit and press Enter; it will open the Registry Editor.
- Search for the key that matches your Outlook version:
Outlook Version Registry Path Outlook 2003 HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\PST Outlook 2007 HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\PST Outlook 2010 HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\PST Outlook 2013 HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\PST Outlook 2016–365 HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\PST - Inside the PST key, right-click an empty area and choose New → DWORD (32-bit) Value.
- Name it MaxLargeFileSize.
- Double-click the new value, select Decimal as the base, and enter your desired maximum size in megabytes. For example, for a 75 GB limit, enter 76800 (75 × 1024).
- Repeat the process to create WarnLargeFileSize. Set this to roughly 95% of your MaxLargeFileSize value, so Outlook warns you before the hard limit is reached — for a 75 GB max, a warning around 70 GB (71680 MB) is reasonable.
- Close Registry Editor and restart Outlook for the changes to take effect.
If you’re still using an older ANSI-format PST file, the equivalent values are MaxFileSize and WarnFileSize, entered in bytes rather than megabytes. Note that ANSI files can only be safely pushed to around 2 GB regardless of these settings — beyond that, the value is effectively ignored and the file becomes a corruption risk.
Important Limitations to Know Before You Do This
- It doesn’t improve performance. A larger PST file limit doesn’t make Outlook faster — if anything, very large PST files tend to slow searching and indexing.
- It increases corruption risk. This is the main reason Microsoft doesn’t officially support pushing PST files past their recommended size. The larger and older a PST file gets, the more fragile it becomes.
- It’s a workaround, not a fix. Raising the limit just delays the point at which you’ll run out of room again. It doesn’t address why the file got that large in the first place.
Safer Alternatives to Raising PST File Size Limit
If you don’t want to alter the registry, you can try the following methods to reduce PST file size without any risk.
- Archive old items: Outlook has a built-in feature called AutoArchive, which moves older emails to a separate archive PST.
File → Tools → Clean Up Old Items (or AutoArchive)
- Compact PST file: When you delete emails or other items, Outlook flags them as deleted, but the PST file size remains the same. Compact Now is a built-in feature to remove these white spaces from the PST file.
Go to File → Account Settings → Data Files, select your file, click Settings → Compact Now.
- Split large PST files: Splitting a large Outlook PST file into a smaller and more manageable file reduces the size of the PST file, thus reducing the risk of corruptions also.
- Remove duplicate items. Repeated sync issues or import errors can leave a mailbox full of duplicate emails, contacts, and calendar items. Cleaning these up can reclaim meaningful space without losing anything you actually need.
What if the PST File Is Already Corrupted?
Oversized PST files are prone to corruption, thus preventing users from accessing emails and other useful data. If the Outlook application is not opening properly, it freezes frequently, or returns errors, it means the Outlook PST file is corrupted. Outlook provides an inbuilt Inbox Repair Tool(Scanpst.exe) to repair minor corruption issues. For severe corruption, it is recommended to use a dedicated Outlook PST Repair Tool such as BLR PST Repair Tool. It is an advanced Outlook PST Repair Tool to repair a corrupt and damaged Outlook PST file instantly. The software is capable of repairing large PST files and recovering emails while maintaining the original properties and folder structure intact. 
Conclusion:
The process to increase Outlook PST file size limit via the registry is straightforward once you understand which values to change. However, this is a short-term fix as increasing the PST file size limit beyond its original recommended limit also pushes it closer to corruption. The bigger PST file size limit also affects Outlook’s functioning, making it freeze more frequently due to the large data file. It is always better to keep a check on the Outlook PST file size by using manual methods such as splitting the PST file, archiving old emails, and compacting the data file from time to time. And if your PST file is already corrupted, you can use Scanpst.exe for minor corruptions and BLR PST Repair Tool for severe PST file corruption.
