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Solve Outlook Data File Reached the Maximum Size Cannot Delete Error

Antonio Gosling ~ July 24, 2025 ~ 8 Minutes Reading

If you are facing the error ‘Outlook data file has reached the maximum size’, it is a common problem. These issues can affect Microsoft Outlook email management, especially when users have crucial mailbox data such as emails, contacts, calendars, and attachments. This error mostly appears when your Outlook file( OST or PST) reaches its higher limit as per your system policies.

Left unresolved, these issues can prevent new emails from syncing, slow down Outlook performance or even cause the application to crash. In this guide, we will break down the causes of this error, how to recognize it early and most importantly how to fix it and prevent it from happening again.

Table of Contents
  1. What Triggers the Outlook Data File Reached the Maximum Size Error? (Causes & Registry Limits)
  2. Signs That Your Outlook Data File Has Reached Maximum Size (Performance slowdown, crashes, sync errors)
  3. Immediate Mitigation Steps to Fix Outlook Data File Has Reached Maximum Size
  4. Manual Solutions to Fix Outlook Data File Reached the Maximum Size
  5. Long‑Term Management Strategies
  6. General Queries
  7. Time to Say Goodbye

What Triggers the Outlook Data File Reached the Maximum Size Error? (Causes & Registry Limits)

  • Historically, size limits varied: Outlook 2002 and older used a 2 GB ANSI format, Outlook 2003-2007 used a 20 GB UNICODE format, and Outlook 2010 and later use a default 50 GB UNICODE format
  • Storing thousands of emails, especially with large attachments, causes your data file to grow rapidly.
  • Without archiving, all emails remain in your primary data file, bloating its size.
  • Your system registry may set lower than maximum file size limits. For example, the keys MaxFileSize, WarnFileSize, or MaxLargeFileSize can override Outlook default and face Outlook data file reached maximum size error.
  • In some cases, data file corruption mimics size limit errors even if the file hasn’t technically hit its cap.

Signs That Your Outlook Data File Has Reached Maximum Size (Performance slowdown, crashes, sync errors)

  • Slow or unresponsive Outlook when sending, receiving or finding emails.
  • The Outlook data file has reached its maximum size, preventing you from sending or receiving emails.
  • Sync issues with Microsoft Exchange or IMAP accounts also indicate that Outlook files have reached their maximum size limit.
  • Unexpected Outlook crashes or freezes on launching also indicate that Outlook data file exceed limits
  • New emails fail to download and remain stuck on the server.
  • Corrupted items or folder missing data unexpectedly.

Immediate Mitigation Steps to Fix Outlook Data File Has Reached Maximum Size

To fix the Outlook data file has reached maximum size error, you can opt for the Jagware PST Splitter This software can easily split any number of Outlook files. It supports advanced filters to export crucial data and breaks oversized Outlook files into smaller, manageable files without any limitations.

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Steps to Fix Outlook Data File Has Reached Maximum Size

  1. Download and run Recommended Software on your pc.
    Outlook Data File Reached the Maximum Size
  2. Click on Configure Outlook mailbox data then tap on Next option.
    Configure Outlook files
  3. Preview to select Outlook mailbox folders as you want to recover.
    Select PST folders
  4. Choose the split options such as split by size, email, date, selected folder in multiple PST and single PST file.
    Browse Split options
  5. Browse destination path and select Advanced filter options.
    Choose destination path
  6. Press Split to start fixing the Outlook data file has reached maximum size.
    Fix Outlook data file reached maximum size

Useful Features of Recommended Tool

  • This software also supports several split options such as split by size, date, email id, split in multiple PST files, and single PST files as needed.
  • It also offers a simple, intuitive interface, making it a reliable tool for all professional and individual users.
  • You can also use Auto detect filter feature to detect Outlook files and also offers to select Outlook files from any custom location.
  • With this wizard, you can also use filter options such as date range, from, to, subject, size, separate PST per user, export only selected Outlook items, create error logs and many more.
  • It also offers you to split unlimited Outlook files without facing any limitations.

Manual Solutions to Fix Outlook Data File Reached the Maximum Size

Once you have confirmed that your Outlook data file is approaching and exceeding its size limit then can follow proven methods to reduce file size, regain Outlook functionality and prevent recurring issues.

Method1. Compact the OST/PST File to Reduce Size

  1. Launch Outlook and navigate to file.
    Open Outlook
  2. Click on Account Settings and again tap on Account Settings in the drop down menu.
    Click on Account Settings
  3. Click on the data files tab and select the oversized PST or OST file.
    Click on data files
  4. Under the advanced tab and click on Outlook data file settings.
  5. Choose Compact Now.
Method2. Enable Automatic Archiving in Outlook
  1. Start Outlook and navigate to file and press on options.
    Click on options
  2. Hit on Advanced and set AutoArchive Settings.
    Click on Advanced
  3. Set how it often runs e.g. every 14 days and choose what items to Archive.
    Run AutoArchive
  4. Enable Permanently Delete old items for trash/junk folders.
Method3. Split Large PST Files into Multiple Smaller Files
  1. Navigate to file and press on Account Settings and choose data files.
    Click on Account Settings
  2. Click on Add to create a New PST file.
    Click on Add
  3. Return to your main Outlook folders.
    Return to Outlook folders
  4. Move older emails, folders or calendar events into new data file via drag and drop.
  5. Once the data is successfully exported to the new PST file, return to your original mailbox and delete the exported items to free up space, then empty your Deleted Items folder.
Method4. Use Import/Export Wizard to Export to a New PST File
  1. Open Outlook and hit on file then choose Open and Export.
    Click on open and export
  2. Select Import/Export and browse Export to a file.
    Click on Export to a file
  3. After clicking on the next option, choose the Outlook file and select the folder to export.
    Select Outlook data file
  4. Set destination and press finish button.
    Outlook data file reached the maximum size solved
Method5. Adjust Size Limits via Registry (MaxFileSize, MaxLargeFileSize)

If your data file is not yet at Outlook official limit(e.g., 50 GB) but you’re still seeing the Outlook data file reach maximum size error, your system may have custom registry settings restricting the file size. You can increase those limits safely by editing the windows registry settings.

  1. Press Win+R and type regedit then press Enter.
    Type Regedit
  2. Navigate to the path: HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\PST
    Select Outlook
  3. Replace version as per your Outlook version and right click on PST file and choose New and DWORD 32-BIT VALUE.
    Click on DWORD(32-bit value)
  4. Add these two file types MAXFILESIZE total size in bytes 100 GB and WARNFILESIZE 95 GB in bytes.
    Set Size Limit
  5. Set both values as decimal and relaunch Outlook.
Long‑Term Management Strategies
  • Auto-Archives moves old items to a separate file. If you are using Microsoft 365, ask your admin to enable Online Archive, which gives you a second mailbox just for old emails, and no more issues about file limit.
  • If you use an Exchange or Microsoft 365 accounts, then navigate to file and click on Account Settings and tap on Choose to keep Mail offline and set it for 6 months or years this way Outlook will store recent messages locally and keep your file size maintained.
  • Empty your Deleted Items, Junk, and Spam folders, and delete unnecessary emails to keep your Outlook file healthy and prevent oversized issues.
  • Sometimes it’s faster to start fresh. Close Outlook, rename your OST file, and reopen the app. Outlook will automatically create a new, fresh OST file that is often smaller and smoother to use
General Queries

What to do When an Outlook Data File is full?

When Outlook reaches a higher limit then you can empty deleted items folder, junk folder and compact data file. If the issues are not resolved then you can increase Outlook file limit using Registry Editor.

How to Increase Outlook Data File Size Limit?

Use Windows Registry Editor to change MAXFILESIZE AND WARNFILESIZE Limit under HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook and relaunch Outlook to apply changes.

How do I Reduce the Size of my Outlook Data File?

Manually delete large or unneeded emails, archive older messages and use the Compact Now feature in Outlook settings. You can also split your PST file for better management.

Why is Outlook Saying My File is Too Big?

Your PST or OST file has likely reached its configured size limit. This can happen due to many emails or attachments available without archiving. After reaching its higher limit, Outlook blocks sending or receiving new emails.

Time to Say Goodbye

Let’s conclude as we have shared all essential information to fix Outlook data file reached maximum size problem. We have top 6 methods to solve this query including manual and its alternative solution. For quicker results, we recommend you to opt Automated Approach as it is specially known for maintained results and no risk of losing any data.