The OST File Has Reached The Maximum Size

Summary: OST file has reached the maximum size is an error message that appears when the size of OST reaches its configured file size or threshold limit. In this guide, we have shared a few fixes and solutions that can help you resolve the OST file size issue in Windows Outlook.

OST or Offline Storage Table is a replica of the user mailbox on the Exchange server. The file is stored on the system locally and syncs the changes made to Outlook with the user mailbox on the server. When the size of OST increases and reaches its threshold or file size limit configured on the system, the error OST file has reached the maximum size may appear.

The error may also appear when the OST file size reaches the configured mailbox size limit on the Exchange server. In such cases, the changes you make are not saved or emails you send are not sent. Similarly, you stop receiving any new mails and face several other issues until you resolve the error. 

How to Resolve OST Has Reached the Maximum Size Error?

One way to resolve the error is to ask the Exchange admin to increase the mailbox size limit. Once the mailbox size is increased, it should probably fix the error.

However, the OST error will soon appear as it reaches the new threshold limit.

But if you control the OST file size, there won’t be a need to increase the mailbox size limit. Thus, we have shared a few methods that will help you reduce the size of the OST file and resolve this issue.

Method 1: Compact OST File to Reduce Size

Outlook has an option to compact .OST and .PST files, which compresses the OST or PST file and reduces the file size. The steps are as follows,

  • Delete any items that you do not want to keep and empty the Deleted Items folder
  • Click File > Account Settings >Account Settings
Find location of OST of file
  • Under the Data Files tab, select the OST data file that you want to compact
  • Click Settings> Advanced > Outlook Data File Settings…
Outlook data file settings...
  • Click Compact Now and then click OK
Outlook OST file location

This will compress the OST file to an extent and may resolve the issue temporarily.

Method 2: Clean Up Mailbox

To fix the issue for a long time, you can choose to clean up your mailbox. However, this method requires you to delete older emails. The steps are as follows,

  • Click the File> Info and click on Cleanup Tools beside Mailbox Cleanup
Options in Outlook to reduce OST size.
  • Click on Mailbox Cleanup… option
cleanup Mailbox in Outlook
  • You can view your current mailbox size stored in local OST file and on the server by clicking on the ‘View Mailbox Size…’ button
Cleanup mailbox to free up space
Check mailbox size and local data volume
  • Enter the number of days to find the older emails and delete them to reduce the size of the OST file and mailbox on the server
  • You can also Find items larger than, Empty Deleted Items folder, View Deleted Items Size, View Conflicts Size, or Empty Conflicts to reduce the OST file size

Further, you can look for large emails, download all the attachments, and then remove the attachments from emails to reduce the OST file size.

Method 3: Use Registry Key to Configure OST File Size Limit

If you don’t want to delete older emails or remove attachments from emails, there’s an alternative way, where you can use the registry to reconfigure the OST file size limits by changing the registry key’s entries and values. There are four registry entries that you can edit and set the maximum size to which OST can grow,

  • MaxLargeFileSize and WarnLargeFileSize

This lets you set the Unicode formatted OST file size limit to a maximum of 50 GB for Outlook 2010 and later or 20 GB for Outlook 2007 and 2003

  • MaxFileSize and WarnFileSize

Refers to the ANSI formatted OST file size limit to a maximum of 2 GB (Outlook 2000)

The following are the default and valid range of ANSI and Unicode formatted OST that you can change.

For Outlook 2019, 2016, 2013 and 2010

NameValid Data RangeDefault
MaxFileSize0x001F4400 – 0x7C0044000×7BB04400 2,075,149,312(1.933 GB)
WarnFileSize0×00042400 –0×7C0044000×74404400 1,950,368,768 (1.816 GB)
MaxLargeFileSize0×00000001 –0×0000C8000×0000C800 51,200 (50 GB)
WarnLargeFileSize0×00000000 –0×0000BE000×0000BE00 48,640 (47.5 GB)

To set the new or reconfigure the OST file size limit, you can refer to this guide on Microsoft Support page.  

Method 4: Move Mail Items from OST to PST or Archive Folder

Instead of deleting older emails, you can move them to a local PST or personal folder file. This can help reduce OST size significantly while keeping all emails intact. To do this, follow these steps,

  • In Outlook 2013, go to File > Cleanup Tools > Archive. In Outlook 2016 or 2019, go to File > Info > Tools > Clean up old items
  • Then select the Archive this folder and all subfolders option
  • Select a folder from the list for archive
  • Then choose the ‘Archive items older than:’ date
  • Click on Browse to choose a save location and click on OK

You can also create a new folder in Outlook and move all emails with large attachments to this folder. Then by following the above steps, archive the folder. This will help you reduce the OST file size and keep large email items.

Also, now that the archive folder is created, you can move more items to this folder manually to keep control on the OST size.

However, it’s important for you to note that the Archives are saved in a personal folder file or PST format. And as you move more and more items in the archive folder, the PST file size will grow larger, which can lead to PST file corruption and data loss.

So, you can either create multiple archive folders to keep PST file size in control or use an OST to PST file converter, such as Stellar Converter for OST, to reduce the OST file size without the risk of PST or data corruption.

Stellar Converter for OST helps you convert the OST file to PST with 100% precision and integrity. After the OST file scan, you can select the mail items or email folders and save them to a PST file. It provides you with filter options that you can use to filter large or older emails and save them to a PST file. While saving PST, it provides the option to compact or split the PST file that helps reduce the PST file size and avoid any corruption.

You can then later add the PST file to your Outlook account and access all the emails with attachments.

Further, the software can help you in times when Outlook becomes inaccessible as your profile is deleted or disabled from the server. It will help you convert and migrate your orphaned OST file data to PST file.


When OST reaches the maximum size, it prevents users from accessing their Outlook email account and restricts communication. To fix this, you can follow the suggested manual methods to reduce the OST file size. You can also convert OST to PST by using a professional OST to PST converter tool. The software features option to split and compact the PST file. This helps keep PST size in the limit as PST files tend to get corrupt or damage when the size grows larger.

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