How to Fix the "Outlook.pst has reached its maximum size" Error?

Outlook stores your mailbox data to a PST – personal Storage Table – on your local device, when you set up your Outlook account with POP3. However, with time and usage, this file becomes large and reaches the recommended file size limit, specifically if you receive a lot of emails large attachments. When the file reaches the recommended size or the limit set by the administrator, you may receive an error message - Outlook.pst has reached its maximum size - when you try to access your account.

This error message, also accompanied by code 0x00040820, may stop you from sending/receiving new emails.

Maximum PST File Size by Outlook Version

Refer the table mentioned below to know the PST file format and size limit that applies to your Outlook version:

Microsoft states that the limits can be configured beyond the documented values; however, increasing them above 50 GB is not recommended because Outlook performance may decrease.

Why Outlook Data File (.pst) Has Reached the Maximum Size?

This error appears when your PST – Personal Storage Table – File reached its defined size limit. This occurs due to one or more of the following reasons:

• Accumulation of emails over time
• Large attachments
• POP3 accounts store mailbox data locally in a PST file, causing the file to grow continuously.
• Retaining deleted items
• Lack of archiving
• Administrator-defined limits

If your PST file reached its defined limit, you may not be able to send or receive new emails.

Methods to fix ‘Outlook.pst has Reached its Maximum Size’ Error

Below, we have mentioned the methods that can help you to fix this error:

Method 1: Archive Old Emails to Free Up PST Space

‘Archive’ feature in Microsoft Outlook that is used to move older email items to a separate Archive.pst file. This helps you to reduce the size of your active PST because it moves items out of the original PST rather than simply marked as deleted. You can use this feature to reduce the size of your mailbox/file, thus resolving the error. Here’s how to do so:

• Open Outlook.
• Go to File > Info.
• Click on Tools > Set Archive Folder.
• Select Archive.
  Select a folder that you want to Archive (e.g., Inbox).

• Now, set a date such as “emails older than 6 months.”
• Click on Browse to choose a destination.
• Click OK. 

Note: Archiving reduces the PST file size only by moving your older emails. If your data file has reached its stipulated size – 50 GB – due to recent, active emails, archiving may not reduce its size limit. In such a case, you can compact your data file.

Method 2: Use Mailbox Cleanup Tool to reduce your PST file size

You can also use Outlook’s Mailbox cleanup feature tool to view the size of your mailbox and individual folders. By using this tool, you can search for older or very large messages that you want to delete or move to a PST file. It helps you to reduce your mailbox size. For more detail check this - Reduce the size of your mailbox.

 You can also use Conversation Clean Up feature in Outlook to remove redundant messages from email threads that contain all of the same information as prior messages. For more information refer to this Microsoft Document. 

Method 3: Compact the PST File using the "Compact Now" Feature

Compacting reduces the size of your PST file by removing blank internal white space left the PST file by deleted emails and other Outlook items. It does not delete any existing mailbox data. Here’s how to do so:

• Open Outlook.
• Click File in the top ribbon.
• Click Account Settings > Account Settings.

• Select the Data Files tab.

• Click on the PST file you want to compact.
• Select Settings.
• In the Outlook Data File tab, click Compact Now.

• Wait for the process to complete. Do not close Outlook while this run.

You can also compact your PST file by right-clicking on your email. Here’s how to do so:

• Right-click your email ID in the Navigation tab.
• Select Outlook Data File Properties.

• Click Advanced.

• Under the Advanced tab, choose Outlook Data File Settings.

• Now click Compact Now.

Note: Compacting only recovers white space from already-deleted items. If your PST file is corrupt, the Compact Now button may fail or hang. In that case, skip to Method 4.

Method 4 - Increase the PST Size Limit via Registry Editor

You can also increase the maximum PST file size limit to fix this error. For this, just create MaxLargeFileSize and WarnLargeFileSize entries via the Registry Editor. 

You can find these registry entries at the following locations:

Below are the steps to increase PST size via Registry Editor:

• Press Windows + R.
• Type regedit.exe and press Enter.

• Click Yes if prompted by UAC.
• Navigate to the path matching your Outlook version (refer the table above).

• If the PST subkey does not exist, right-click Outlook, choose New > Key,
• Then, name it PST.
• In the right panel, right-click on empty space and choose New.
•  Click DWORD (32-bit) Value.

• Name the new value MaxLargeFileSize. 
• Press Enter.
• Double-click MaxLargeFileSize.
• Select Decimal.
•  Enter the value in megabytes. For 100 GB, enter 102400.
• Click OK.

Now, create WarnLargeFileSize value by repeating the Steps 3–5. You have to set this to about 95% of MaxLargeFileSize value (For example; 97280 for 95 GB).

Close Registry Editor and restart Microsoft Outlook.

The new size limit is now active.

Note: It is only a short-term fix. If your PST file reaches 100 GB, Outlook will perform slowly. It may also increase the risk of file corruption.

Method 5: Repair/Split the Oversized PST File

If your PST file gets corrupted due to large size or any other cause, then you can go for an advanced solution. You can use Stellar Repair for Outlook. This tool can repair severely corrupted or large PST files. It’s Auto Split feature split resultant file within the 50 GB default size limit into multiple smaller parts.

Here are some notable features of this tool:

• Recover all mailbox items - emails, attachments, contacts, calendars, tasks, notes, etc.
• Shows preview of all recoverable items after repair.
• Option to include or exclude specific emails while saving repaired PST file.
• Restores mailbox items to a new PST file.
• Saves repaired items in EML, MSG, RTF, HTML, or PDF file.
• Supports MS Outlook 2024, 2021, 2019, and earlier versions.
• Export repaired PST to Microsoft 365 or live Exchange Server.
• Provides Auto Split feature to split large PST file. 

Watch the below video to know how Stellar Repair for Outlook works:

Conclusion

You can resolve the error "Outlook.pst has reached its maximum size" by reducing the file size. You can follow the different methods - mentioned in this guide - to do so. If your file is oversized and corrupted, use Stellar Repair for Outlook to repair it. This can also split the repaired file into multiple smaller parts.