How Do I Reduce the Size of an Outlook data file?

An Outlook data file is also known as Offline Storage Table file that is a data storage file created by Microsoft Outlook. It usually maintains a copy of the mailbox data from an Office 365, Exchange, or Outlook account. When online, it syncs with the server after being saved on the local computer. By using this data file, emails can be viewed and erased even when the user is not connected to the internet. Once Outlook is online, changes will be saved in the storage file and updated on the server. Users frequently continue to communicate for years without giving their mailbox size any thought. Offline storage keeps growing until it reaches its maximum size which results in bugs, failures, and hangs in Outlook email clients and may also corrupt the Outlook data file. In this post, we will discuss methods for reducing the size of the Outlook data file.

Why Large Outlook data Files (OST&PST) Creates An Issue?

An Outlook data file is dependent on the synchronization principle. As long as it will take to sync with the online sever, there are chances of Outlook sync issues that will increase with the size of the Outlook data file. 

The larger the Outlook data file, the longer it will take to check the data integrity. It is also possible that Outlook will get stopped when checking the integrity, which is known as the “Outlook held at verifying data integrity error”.

Issues that can be caused by a large OST/PST file:

• The OST/PST file cannot be accessed.
• To an existing Exchange .ost file, any data cannot be added.
• The MS Outlook hangs or stops.
• During the synchronization process, some error message can occur.

Note: By default, Outlook version 2007 and 2003 has a file size limit of 20 GB and Outlook 2010, 2013, 2016, and 2019 the file size limit of 50 GB.

Methods for Reducing the OST/PST File Size

Here we have listed some methods to reduce the size of the OST/PST file if you are experiencing an issue when using MS Outlook.

Clean Up the Mailbox Data

Unwanted and obsolete emails can be a reason for the large size OST/PST file. To clean up the mailbox data, follow the measures below:

• Open Outlook >go to File tab and click on Info tab > then click on cleanup tools besides mailbox cleanup.
• Click on Mailbox Cleanup.
• In mailbox dialog box, hit on View mailbox size option to see your current mailbox size that is stored in the local OST file.
• After viewing the data, enter the number of days to find the older emails and delete them.
• Finally, complete the process by clicking on the Close button.

Moreover, to minimize the size of the OST/PST file, user can look for emails with the large attachments, download them, and afterwards remove the attachments from the emails.

Compact the Size of the OST File

MS Outlook comes with an option called Compact that lets the user to compact the file size of both OST and PST. Take a look on the following procedure below:

• Open File tab and click on Account Settings >choose Account Settings option.
• In Data Files tab, choose the necessary Outlook Data file.
• Click on Settings > Advanced then, click on Outlook Data File Settings
• Select Compact Now option and hit the OK button.

Note: This method permits you to fix the problem temporarily only by compressing the selected OST file to a particular level.

Sharing the Information Via Shared Folders

The “Shared Folders” makes the user able to maintain their data or information with other Exchange accounts. It needs to be disabled as they take a lot of space in the OST file. Look into the following steps to stop Outlook from compressing the OST file and the shared folders synchronization:

• In Outlook > Go to File tab > Account Settings > Click on Account Settings.
• Click on the Data Files tab and choose the OST file that you want to shrink.
• Open Settings > Go on Advanced > then Outlook Data File Settings option
• Disable the button Download Shared Folders and click OK. 

Now restart the Outlook account for re-synchronization of the files.

Set up Archive Folder Manually

Whenever you wish, you can manually archive files. The user can decide which mailbox content to archive, where to store them, and how old a mailbox content must be before it can be archived.

Select one of these:

• In Outlook 2013: Go to File > Info > Cleanup Tools > Archive
• In Outlook 2016: Go to File > Info > Tools > Clean up old items

Note: If your mail profile is connected to an Exchange Server, Archive and Auto Archive it might not be accessible. Another possibility is that your company has a mail retention policy that replaces Auto Archive. For further information, contact your system administrator.

• Go to Archive this folder and all subfolders option, and select the folder you wish to archive.
• Then under Archive items older than, enter a date.
• You can make multiple .pst files if you want to archive few folders using different settings.
• To archive certain things that are exempt from automated archiving, click on Include items with the “Do not Auto Archive” option. This option ignores the Do not Auto Archive setting for this archive only rather than removing that exclusion from those items.
• Click OK.

Turn off Auto Archive

Turn off Auto Archive to only archive when you wish to.

• Click File > Options > Advanced.
• In Auto Archive, click on Auto Archive Settings.
• Uncheck the Run Auto Archive every n day’s box.

Configure File Size Limits With the Help of Registry Key

User can remove the older emails and email attachments without deleting them to resolve the OST file size issue. By altering the registry key’s entries and values, you can change the OST file size limitations. Let’s take a closer look at below registry entries:

• MaxFileSize registry entry
• WarnFileSize registry entry
• MaxLargeFileSize registry entry
• WarnLargeFileSize registry entry

The ANSI and Unicode formatted OST’s default and permitted range are listed below.

For Outlook 2010, 2013, 2016, and 2019

Final Words

The majority of users have faced the problem of Outlook data file has increased too large. We have provided some methods above mentioned to resolve the issue of large files in OST & PST file. You can expand the PST file size without any problems by using this method, which will assist you in making the right decision. A reliable fix for this Outlook data file that has exceeded the maximum size issue is an automated solution.