Reduce OST File Size in Outlook: Clean Up Outlook Mailbox

How to Check Your Current OST File Size

This shows the current location and size of your OST file:

• Firstly, open Outlook on your PC.
• Now, go to File > Account Settings > Account Settings.
• After that, click the Data Files tab.
• Select your OST file and choose Open File Location.

Instant Step to Reduce OST File Size in Outlook

1. Download and install the DRS OST File Splitter.
2. Click on Add Files to load your OST file. Click Next.
3. Select the different Splitting options. Press Next.
4. Lastly, choose the Split OST file Size and location. Click Split.

Why You Should Compact OST File Size in Outlook

Here are the main reasons to reduce your OST file size:

• Improve Outlook Speed: A smaller OST file helps Outlook open and respond faster.
• Fix Sync Errors: Large OST files often fail to sync properly with the server.
• Avoid Errors: Outlook can show messages saying the data file has reached its maximum size.
• Free Up Disk Space:  Smaller OST files save space on your hard drive.

Manual Methods to Reduce OST File Size in Outlook

Manual methods allow you to reduce the OST file size using built-in Outlook features. These methods are safe, cost-free, and suitable for users who want full control over their mailbox data.

Delete Unnecessary Emails and Attachments

One of the easiest ways to reduce OST size is by removing emails you don’t need:

• Remove old or unread messages.
• Delete emails with large attachments you already saved elsewhere.
• Empty the Deleted Items folder to permanently remove deleted emails.

Tip: After deleting, Outlook won’t immediately shrink the OST file; you need to compact it manually.

Empty Deleted Items and Junk Folders

Even after deleting emails, those messages may remain in your Deleted Items or Junk folders. Empty both folders completely:

• Go to the Deleted Items folder.
• Right-click and choose Empty Folder.
• Do the same for Junk Email.

Compact Outlook Data File in Outlook

Compact is a built-in Outlook feature that permanently removes space left after deleting emails. Steps to Compact OST File:

• Go to File > Account Settings > Account Settings.
• Afterwards, click the Data Files tab.
• Next, select your OST file.
• Then, click Settings.
• Under Advanced, choose Outlook Data File Settings.
• In the end, click Compact Now.

Archive Older Emails

Instead of deleting older emails, you can move them to an archive file (.PST):

• Go to File > Info.
• Choose Tools > Clean Up Old Items.
• Select a folder to archive and a date (e.g., emails older than 1 year).
• Choose a location and click OK.

Archiving moves old emails out of the OST file, which reduces its size.

Adjust Synchronization Settings

Outlook lets you limit how much mail it downloads and stores locally:

• Start by going to File > Account Settings > Account Settings.
• Double-click your email account.
• Change Mail to keep offline (for example: from “All” to 6 months or 1 year).

Disable Shared Folder Sync

If you access shared mailboxes or shared folders, Outlook may cache them in your OST file, increasing its size:

• Go to File > Account Settings > Account Settings.
• Under Data Files, select your OST file.
• Next, choose Settings > Advanced.
• Uncheck Download Shared Folders.
• Finally, restart Outlook.

A Reliable Tool to Reduce OST File Size in Outlook

The DRS OST Splitter Tool is a professional tool to handle your large OST file effectively. This is a compact, fast, and error-free solution. You can split multiple or large OST files at once without any restrictions. Offer several splitting features, like Split based on Date, Size, Sender, and Folder. The demo version is available to evaluate its features, and you can split 50 emails per folder. Designed with a simple interface, which means every user can easily use it without needing any technical skills. Also, it is highly compatible with all Windows and Mac versions.

Verified Steps to Reduce OST File Size in Outlook

1. Primarily, launch the DRS OST File Splitter Tool on your PC.
2. Click on the Add File to add the desired file and then hit Next.
3. Select the files/folders and choose the splitting criteria. Click Next.
4. Then, choose the Size of the resultant OST file and define the Path to Save.
5. Lastly, click Split to complete the procedure of splitting the OST file.

Is the DRS Tool Safe to Reduce OST File Size in Microsoft Outlook?

Yes, the DRS Tool is safe to use for reducing OST file size in Microsoft Outlook. It is widely recommended by IT professionals and email experts because it works securely. Ensures that your original mailbox data remains unchanged while the size reduction process is performed.

Conclusion

In this technical blog, we explored several methods to reduce OST File size in Outlook. The manual methods are freely available, but they do not provide a guarantee of secure results. That’s where we also discussed the DRS professional tool. It splits multiple OST files simultaneously without any data loss. Preserves the original data formatting, structure, and metadata during the entire process. So, download this tool and securely split your OST file. If you have any questions related to this tool, feel free to ask our technical support.

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