Fix “Outlook Data File Has Reached Maximum Size” Error in Outlook

Ritu Roy | fix How to's Outlook outlook error Software Technology | 9 minutes read | Modified on: 11-03-2026

Introduction: Microsoft Outlook stores mailbox information such as emails, contacts, calendars, tasks, and other data in special files known as PST (Personal Storage Table) and OST (Offline Storage Table) files. These files help Outlook manage and access your data efficiently, whether you are working online or offline.

However, as you continue using Outlook over time, these data files gradually increase in size. When a PST or OST file reaches its maximum storage limit, Outlook may start experiencing performance problems. Users might notice issues such as difficulty sending or receiving emails, error messages appearing frequently, slow performance, or even unexpected application crashes. One of the common problems Windows users encounter in such cases is the “Outlook Data File Reached Maximum Limit” error.

Although users on macOS may not always see the same warning message, they can still experience similar issues when Outlook data files grow too large.

In this article, we will explore practical solutions to resolve this error. The guide will walk you through effective methods to reduce the data file size and restore Outlook’s normal functionality safely.

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

The “Outlook Data File Reached Maximum Limit” error occurs when an Outlook data file, either a PST or OST file, has grown to the maximum size allowed by the application. Once this limit is reached, Outlook cannot store any additional data in that file. As a result, the program may struggle to function properly, and several performance issues can start to appear.

When this problem occurs, Outlook is essentially informing the user that the data file is full and cannot accept new emails or other mailbox items until the file size is reduced or managed.

Common Effects of This Error

When the Outlook data file reaches its maximum capacity, users may experience the following problems:

Outlook displays warnings related to the data file size limit.
The application becomes slow or stops responding.
Sending or receiving emails may fail.
Outlook may crash or freeze frequently.
New emails might not download or sync properly.
Some emails may not appear in the inbox or other folders.

These issues can significantly disrupt email communication and productivity, making it important to address the problem as soon as possible.

Why Does Outlook Data Reach the Maximum Size?

Outlook data files gradually grow over time as more emails and mailbox items are stored. Several factors can contribute to a PST or OST file reaching its maximum size limit. Some of the common reasons include:

Accumulation of emails over many years, which significantly increases the size of the Outlook data file.
Large email attachments, such as documents, images, and videos, consume a considerable amount of storage space.
Items in the Deleted folder that are not permanently removed continue to occupy space in the data file.
Frequent backups or data storage within the same PST file causes the file size to expand rapidly.

When these factors combine, the Outlook data file can eventually reach the maximum size allowed by the application.

Outlook Data Files and Their Size Limitations

Outlook stores mailbox information in two main types of data files: PST (Personal Storage Table) and OST (Offline Storage Table). These files contain essential mailbox components such as emails, attachments, contacts, calendars, tasks, and notes.

PST Files

A PST file is used to store Outlook data locally on a user’s computer. It is commonly used when emails are downloaded from the server, especially with POP email accounts. PST files are also widely used for creating backups or archiving old mailbox data.

One advantage of PST files is that they are flexible and portable. Users can easily copy, move, import, or export PST files between systems or Outlook profiles, giving them full control over their stored data.

OST Files

An OST file is created when Outlook is configured with accounts such as IMAP, Microsoft Exchange, Outlook.com, or Office 365. This file stores a local copy of the mailbox so users can access their emails and other data even when they are offline.

When an internet connection becomes available again, Outlook automatically synchronizes the OST file with the mail server, ensuring that all updates are reflected in the mailbox.

Unlike PST files, OST files are linked to a specific Outlook profile and cannot be opened directly on another system without the associated account configuration. Their primary purpose is to provide a cached copy of mailbox data, which improves Outlook’s performance and allows faster access to emails and other information.

Standard Size Limits of Outlook Data Files

Each version of Outlook has a predefined limit for the size of its data files. These limits apply to both PST and OST files and depend on the format used by the specific Outlook version. Understanding these limits can help users manage their mailbox data and avoid performance problems.

Below is an overview of the common size limits for Outlook data files:

Outlook Version	Data File Format	Maximum Size
Outlook 2002 and earlier	ANSI	2 GB
Outlook 2007 – Outlook 2010	Unicode	20 GB (default limit)
Outlook 2013 – Outlook 2016	Unicode	50 GB
Outlook 2019 / Outlook 2021 / Microsoft 365	Unicode	50 GB

Important Note: Even though newer Outlook versions allow data files up to 50 GB, performance issues may appear before reaching this limit. Outlook may start displaying warnings or experience slow performance once the data file grows close to its maximum capacity. For this reason, it is recommended to regularly manage and reduce the mailbox size to prevent potential problems.

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

Troubleshooting Steps to Resolve the “Outlook Data File Reached Maximum Limit” Error

If your Outlook data file has reached its maximum size, there are several methods you can try to reduce the file size and restore Outlook’s normal performance. Below are some practical solutions, ranging from basic cleanup steps to more advanced options.

Solution 1: Remove Unnecessary Emails and Attachments

One of the quickest ways to reduce the size of an Outlook data file is by deleting emails that are no longer needed. Messages with large attachments often take up a significant amount of storage space.

You can manage this by:

Sort your emails by size to identify the largest messages.
Deleting emails that contain large or unnecessary attachments.
Clearing the Deleted Items folder to permanently remove deleted emails.
Emptying the Junk Email folder to free additional space.

You can also use Outlook’s search filter to quickly locate large emails. For example, using a filter such as Size: >10 MB helps you find messages that consume the most storage so they can be reviewed or removed.

Solution 2: Archive Old Emails

Archiving older emails is another effective way to reduce the size of your active Outlook data file. By moving older messages to a separate archive file, you can keep your primary mailbox smaller while still retaining access to important data.

Steps to archive emails manually:

Open Outlook and go to File.
Select Tools, then choose Clean Up Old Items.
Choose the folder you want to archive.
Specify the date range for older emails.
Save the archived data to a new PST file.

Outlook also offers an AutoArchive feature that can automatically move older emails to an archive file at regular intervals.

To enable AutoArchive:

Go to File > Options.
Select Advanced.
Click AutoArchive Settings.
Configure the schedule and archiving options according to your preference.

Archiving helps maintain Outlook’s performance by keeping the active data file smaller while preserving older emails for future reference.

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

If deleting unnecessary emails or archiving old data does not fully resolve the issue, you can try compacting the Outlook data file. Compacting helps reclaim unused space within the PST or OST file that may remain after items have been deleted or moved. This process can reduce the overall file size and improve Outlook’s performance.

Steps to Compact PST or OST Files

Follow these steps to compact your Outlook data file:

Open the Outlook application on your system.
Click on File in the top menu.
Select Account Settings, then choose Account Settings again from the dropdown.
Go to the Data Files tab.
Select the PST or OST file you want to reduce in size.
Click Settings, then choose Compact Now.

The time required for this process depends on the size of the data file. Larger files may take longer to compact, so it’s best to allow the process to complete without interruption.

Solution 4: Split the Data File to Resolve the “Outlook Data File Reached Maximum Limit” Error

When a PST file becomes excessively large, splitting it into smaller files can be an effective long-term solution. Large data files not only increase the risk of reaching the maximum size limit but can also slow down Outlook’s overall performance. By dividing a large PST file into multiple smaller files, users can manage their mailbox data more efficiently.

Separating the data into smaller parts helps improve Outlook’s speed and stability. It also makes tasks such as searching, backing up, and organizing mailbox data much easier.

To perform this task, users can utilize a PST File Splitter tool, which allows them to divide the large PST file into smaller segments based on a preferred size or other criteria. This approach ensures better data management while preventing the Outlook data file from reaching its maximum storage limit again.

Solution 5: Repair the Outlook Data File Using ScanPST

Microsoft Outlook provides a built-in repair utility known as the Inbox Repair Tool (ScanPST). This tool is designed to detect and fix minor issues within PST files that may cause errors or affect Outlook’s performance.

Steps to Repair an Outlook Data File

Follow these steps to repair a PST file using ScanPST:

Close the Outlook application.
Locate the SCANPST.EXE file on your computer. This file is usually found in the Outlook installation folder.
Open the tool and click Browse to select the PST file you want to repair.
Click Start to begin scanning the file for errors.
If issues are detected, select Repair to fix them.

The ScanPST utility is useful for resolving minor corruption or structural issues within Outlook data files. However, it may not always be effective for severe corruption or very large PST files.

Solution 6: Increase the PST File Size Limit

Another possible approach is to increase the maximum size limit of the PST file through the Windows Registry. This method allows Outlook to handle larger data files, which may temporarily resolve the “Outlook Data File Reached Maximum Limit” error.

Important: Editing the Windows Registry should be done carefully. Incorrect changes can affect system performance or cause other issues. It is recommended to create a backup of the registry before making any modifications.

Registry Keys Used to Modify PST Size Limits

Two main registry keys control the PST file size limit:

MaxLargeFileSize – Defines the absolute maximum size allowed for a PST file.
WarnLargeFileSize – Determines the size at which Outlook begins displaying warning messages.

By adjusting these values, users can increase the PST file size limit. However, even though the limit can technically be extended (for example, up to around 50 GB in newer Outlook versions), Microsoft generally does not recommend significantly increasing the limit because very large PST files may lead to performance problems and a higher risk of file corruption.

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

When manual methods are not sufficient to resolve the issue, using a professional solution can be a more efficient approach. Large PST files can be difficult to manage, and advanced tools are specifically designed to handle such situations safely and effectively.

A PST Converter or similar professional utility can help reduce the size of large Outlook data files by allowing users to export or migrate mailbox data to another format or email platform. Instead of keeping all the data within a single PST file, the tool enables you to transfer selected emails and other mailbox items to a different destination, which helps prevent the file from reaching its size limit again.

Conclusion

The “Outlook Data File Reached Maximum Limit” error is a common issue that many Outlook users encounter when their mailbox data grows too large. Although this problem can affect Outlook’s performance and prevent normal email operations, it can be resolved with the right approach.

Users can manage this issue through several methods, such as deleting unnecessary emails, archiving older messages, compacting the data file, or splitting large PST files into smaller ones. In cases where manual solutions are not sufficient, professional tools can help manage or migrate Outlook data more efficiently.

The key is to address the problem early, before the data file becomes excessively large or risks corruption. By following the solutions discussed in this guide, users can effectively reduce the size of their Outlook data files and maintain smooth email performance.