How to Reduce OST File Size in Outlook

Updated On - December 1, 2022 by Armaan |

Reading Time: 6 minutes

Outlook’s OST file is an offline storage archive replicating Exchange Server mailboxes. It stores data locally and automatically updates itself anytime whenever the user is connect to the internet. Utilizing this data file allows messages to be viewed and deleted even when one is not connected to the internet. All time Outlook is connected to the internet, any changes made to the local storage file will be synchronized with the server. People frequently continue communicating for years without ever upgrading their inboxes. Data sizes in offline storage eventually exceed available space. This results in malfunctions and freezes the Outlook email client and may cause OST file corruption. Data saved in a storage file requires prompt action to reduce the likelihood of failure. As a result, this essay covered a few methods to reduce OST file size in Outlook.

Regular Maintenance to Reduce OST file size in Outlook

Emails, contacts, calendars, notes, journals, tasks, and so on can all be store in one convenient place by using an OST file. All of the mailbox information makes up the bulk of the OST file. By keeping up with mailbox cleaning, you can prevent the offline storage quota from being exceeded. Thus, the potential for corruption is minimize. Checking OST file size can be done in a few different ways.

  • Frequently deleting old messages and other junk from the inbox.
  • Clear up your trash and spam folders, so your offline folder file doesn’t get too big (.ost).
  • When erasing mail from a mailbox, you should always choose the “hard delete” option.
  • It’s important to condense your mailbox folders regularly.

Why do OST files get so big?

Since you set up your Outlook account, all your outgoing and incoming messages have been save in an OST file. It incorporates everything from emails (in various folders) to calendar events, tasks, contacts, notes, secret files, public folders, and so on. The OST file and Outlook will experience corruption if unnecessary data accumulates to the point where the file’s storage capacity is exceed. It’s not just email with huge attachments that can balloon your OST file’s size.

Some Manual Solutions to Reduce OST file Size in Outlook

Overly large OST files cause problems in Outlook, including:

  • The inability to open or load the associated.ost document.
  • Cannot append new information to an already-created Exchange. Ost file.
  • Interruptions in Microsoft Outlook.
  • Messages of failure during the synchronization procedure.
  • Inability to resolve problems with OST file synchronization with Microsoft Exchange Server.

Solution Procedures for “Oversized” OST File Errors

Simple Tasks: To manually remove unnecessary or unwanted information from the OST file, follow these key actions or methods.

  • Clear up your OST inboxes of outdated messages for good!
  • Make sure the Deleted Items folder in the OST mailbox is empty
  • Move the OST file from its default location
  • Rename the file; let it be generated again if it contains important or huge attachments.

Inactivating all plug-ins:

Several Outlook add-ons have been shown to impede the program’s efficiency. Disabling Add-Ons is a good choice if you want to speed up Outlook. If you want to do this, here are the steps you need to take:

  • First, open Outlook and navigate to the File menu, then Options, and finally, Add-Ins. 1
  • Click the Go button next to COM Add-Ins in the Manage section.2
  • Click the OK button, then deselect all the plug-ins that aren’t being used right now. 3

Archive OST file data: The data in an OST file could be reduced in size and server space freed up by archiving the file’s contents. The location of the archived OST file can be moved to a new directory. By archiving your OST file, you can keep it from growing above a certain size. This document contains instructions on how to archive it.

    1. Open your inbox by going to the File menu, clicking Cleanup Tools, and finally choosing Mailbox Cleanup. 4
    2. Next, you can choose between two alternatives:
      • With the help of the AutoArchive feature, older mail can be automatically moved to a separate archive folder.
      • Empty the trash by erasing anything in the Trash folder.

Use Outlook’s built-in compression feature:

You can shrink your OST file and make it more manageable. A smaller file size may improve Outlook’s speed if the user has deleted numerous items. Use the provided procedures to compact your OST file.

  • First, get rid of anything that is no longer needed.
  • Then, in the Navigation pane, open the folder’s list view, right-click on the folder, select Deleted items, and finally select Empty folder.
  • Click the File tab, then pick Account Settings from the drop-down menu.
  • Select the data file you want to condense under the Data Files tab, then click the Settings button. 5
  • The Outlook Options dialog box will open; navigate to the Advanced tab and select Outlook Data File Settings. 6
  • The last step is to click Compact Now in the Outlook Data File Settings dialogue box. 7

Limit the Size of OST Files using a Registry Key

Suppose you don’t want to delete older emails or remove attachments from emails. In that case, 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. Limits on OST expansion can be specified by modifying four separate registry items.

Move OST file data into PST format using Regain OST to PST converter.

Apart from above mentioned manual solutions, several Outlook users and professionals suggest using Regain OST Converter tool. The tool is coded by professionals and eases the process of OST to PST conversion.

Free Download100% Secure Buy NowPrice: $39

There is no requirement for technical assistance and expertise to use the tool, and even a newbie can use this tool to convert OST files into PST format and get rid of large-size OST files. The good thing about this tool is it also has a PST split option. Hence, you can pick a desired file size for the resultant PST file. Let me show you how you can convert OST to PST using Regain software.

Words for attention: Before diving into the process, make sure to download the free OST to PST converter tool.

  • Firstly, open the OST to PST converter in your system.
  • Click on the Open option from the ribbon bar.
  • Now add OST large-size files you want to convert into PST.
  • Following, click on the Export option from the ribbon bar.
  • Choose the PST file format option in the next wizard.
  • Select PST size and click on the convert now option.

Voila, you’ll have a PST file of your OST file and can access it in any Outlook version. Also, you can do the process in any Windows operating system.


When the OST storage volume hits its limit, Outlook email accounts become inaccessible. To solve this problem, try manually decreasing the OST file size. A reliable OST to PST converter tool is also available for those interested in making the switch. The PST file can be divided and compressed using the program’s available options. Since PST files frequently get corrupt or corrupted when their size increases, this helps keep PST size under the limit.

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