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How to Fix “Outlook Data File Reached Maximum Limit”?

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Jamie Kaler   Contribution
Rollins Duke
Rollins Duke  Approved By
Published On February 3rd, 2026 • 7 min read

Microsoft Outlook use data files to store the emails, contacts, calendar items, tasks, and other mailbox information. The files are PST (Personal Storage Table) and OST (offline storage Table) files. Over time, as we use the application, the Outlook data file may reach its maximum size limit. When this happens, the Outlook won’t be able to perform the task it already did, which is sending/ receiving emails, and will show error messages, freeze and even crash. “Outlook Data File Reached Maximum Limit” is one of the most common errors faced by Windows Outlook users. While macOS users do not see an exact warning message, but does face similar storage-related issues.

The article here provides a proper solution to overcome this error, with all the steps explained properly to fix it safely.

What does “Outlook Data File Reached Maximum Limit” Error Mean?

The error is as it says, that the Outlook files, PST or OST file has reached their maximum size allowed by Outlook. Whenever such an error occurs, is warning the users that new data cannot be added. What are the outcomes of this error:

  • Outlook display a warning about the data file size.
  • Being slow or unresponsive.
  • Outlook is unable to send or receive emails.
  • Frequently crashed or froze
  • New emails fail to download properly.

How Does Outlook Data Reach the Maximum Size?

The reason can vary and can happen due to many issues.

  • Years of emails accumulate and could lead to oversized Outlook data files.
  • Large email attachments can also lead to an increase in Outlook files.
  • The deleted files are not completely removed.
  • If there is a frequent backup within the same PST files.

Outlook Data File & Its Size Limitations

Outlook Files are PST & OST files, and the files contain important information such as emails, contacts, attachments, calendar, tasks, and notes.

PST files store Outlook data when the emails are downloaded locally. It is commonly used to create backups and for archiving of the POP accounts. The user can copy, move or import the PST files, giving them complete control.

OST files are created when Outlook is configured with an IMAP, Exchange or Office 365 account. As the name says, it allows users to access the mailbox data offline, and when back online, it automatically syncs with the mail server. However, an  OST file cannot be opened without the specific Outlook profile, unlike a PST.

OST files are data files are stores localy copy of the mailbox when we use Outlook with email servers like Microsoft Exchange, Outlook.com or Office 365. It lets users access the Outlook data, such as emails, contacts, calendar, etc., offline. If you made any changes, it automatically syncs when connected to the internet. It makes Outlook work faster by keeping a cache copy of mailbox data.

Here are the standard size limits of the Outlook Data files:

Outlook Version PST/OST Maximus Size
Outlook 2002 & earlier ANSI 2 GB
Outlook 2007–2010 Unicode 20 GB (default)
Outlook 2013–2016 Unicode 50 GB
Outlook 2019 / 2021 / Microsoft 365 Unicode 50 GB

Note: Even though we have a maximum limit of 50GB, the warning message could show before that and will affect the performance of Outlook.

Check out the related article: Why is the Outlook OST file so large?

Troubleshooting Steps: Resolve Outlook Data File Reached Maximum Limit

Here are some of the common to advanced approaches that can be used to overcome the oversized Outlook data files.

Solution 1: Delete Unnecessary Emails and Attachments 

Reducing the mailbox size is the first and direct fix we can do:

  1. Sort the emails by size.
  2. Delete emails with large attachments.
  3. Empty the Deleted Items folder
  4. Or, Empty Junk Email folder

Use the Filter: Size:>10MB to locate large emails instantly.

Solution 2: Archive OLM Emails

We can archive the old data to a separate file to reduce the size of the active PST file.

How to steps:

  1. Go to File > Tools > Clean Up Old Items.
  2. Choose the folder to archive.
  3. Then, select the data.
  4. Save the archive to a new PST file.

There is also an option to do auto archive:

Go to File > Options > Advanced > AutoArchive Settings.

Solution 3: Compact File to Fix “Outlook Data File Reached Maximum Limit” Error

Even after deleting or archiving, if the error is not resolved, then we can compact the Outlook data to reclaim the storage space.

Steps to Compact PST/OST File:

How to compact Outlook data files-

  1. Start the Outlook application.
  2. Go to File > Account Settings.
  3. Select the Data Files tab.
  4. Now, select PST/OST, then click Settings.
  5. Click on Compact Now.

Depending on the size of the files, the process will take time.

Solution 4: Split the Data Files & Resolve – Outlook Data File Reached Maximum Limit

If the PST files are large files, then splitting the files into smaller parts is a safer long-term solution. The benefits of this method are that it improves the Outlook performance, making it easier for data managment.

Use the PST File Splitter to divide the files into the desired size as per the user’s requirement.

Solution 5: Repair Outlook Data File with ScanPST

Outlook has built in repair tool to repair the Outlook data file.

Steps to repair the Outlook data file:

  1. Click the Outlook.
  2. Locate SCANPST.EXE.
  3. Browse and select the PST file.
  4. Click Start and then the Repair button.
  5. The ScanPST works for these types of minor issues.
Solution 6: Increase PST File Size Limit

We can use the Windows Registry to manually increase the size of the Outlook data file if the Outlook Data File Reached Maximum Limit.

Note: Proceed carefully as incorrect Registry edits can cause other system issues.

Registry Keys

  • MarLargeFileSize
  • WarnLargeFileSize

We have an option to increase the limit to 50GB, but Microsoft does not recommend this due to the performance risks.

Solution 7: Use a Professional Tool to Fix “Outlook Data File Reached Maximum Limit”

As we said before, the better option is to use a splitting tool or a tool to back up the Outlook data file to another email client. For that, we can use PST File Converter.  These tools help to reduce the file size, ensure smooth transfer of emails and other mailbox items. Additionally, both tools allow batch processing to make the process faster and more efficient.

FAQs

Is it possible to increase the size of the Outlook PST file?

Yes, it is possible to increase the size limit of the Outlook PST file with the Windows Registry settings. Since the method would impact Outlook’s performance and increase file corruption, it is not recommended like other methods. It is better to reduce the size of the file rather than increase the Outlook data file size.

What happen of the Outlook data file if it exceeds the maximum limit?

When the Outlook data file exceeds its limit, the application will slow down, crach or freeze frequently. User might face other issues liek unable to send or receive emails or even data corruption.

Does deleting emails fix the “Outlook Data file reached maximum limit” error?

Yes, deleting the unwanted emails entirely from the account could fix the Outlook data file exceeding the maximum size limit.

Conclusion

The error message “Outlook data file reached maximum limit” is very common but completely manageable. There are different solutions that users can choose from manual cleanup, Outlook data compact, or using professional solutions. The most important aspect here is to act before there is any file corruption occurs. Follow the steps in the article here to fix the issue instantly.