How to Increase OST File Size in Outlook 2013 & After Edition

When you utilize Exchange, Office 365, or IMAP accounts with Microsoft Outlook, it stores synced mailbox data in Offline Storage Table (OST) files. OST files let people read their emails, contacts, calendars, and other mailbox contents even when they are not connected to the internet. But Outlook versions from 2013 and beyond have limits on how big OST files may be. 

Learn about the limits on the size of OST files

The Unicode OST format is used by Outlook 2013, 2016, 2019, and Microsoft 365. It can handle files up to 50 GB in size by default. Most people can live with this limit, but businesses that send a lot of emails or have big attachments typically go over it. Outlook may cease syncing fresh emails and users may notice a drop in speed when the OST file exceeds its maximum size.

The Toolsbaer OST to PST Conversion , you need to change several settings in the Windows Registry. Before making any changes, you should take certain safety steps, such backing up your registry data and making sure Outlook is closed.

Method 1: Use the Windows Registry to make the OST file bigger

If you want to raise the OST file size restriction in Outlook 2013 and later, follow these procedures closely.

Step 1: Shut off Microsoft Outlook

Before changing the registry, make sure Outlook is entirely closed to avoid problems.

Step 2: Start the Windows Registry Editor

Press Windows + R to launch the Run box.

Press Enter after typing regedit.

If asked, click Yes to let the changes happen.

Step 3: Go to the Outlook Registry Path

For Outlook 2013, go to the following place:

HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\PST

For Outlook 2016 and later, use:

HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\PST

Step 4: Make new or change existing registry values

In the PST folder, make new DWORD values or change the ones that are already there:

MaxLargeFileSize sets the largest size for an OST file.

WarnLargeFileSize sets the limit for the warning before the file reaches its maximum size.

Choose New → DWORD (32-bit) Value from the right-click menu in the right panel. Give it a name that makes sense.

Step 5: Limit the Size of Files

You have to provide the quantities in megabytes (MB). For example:

61440 MB = 60 GB

80 GB = 81920 MB

To change the size, double-click each DWORD and type in the size you want in Decimal format.

Step 6: Open Outlook again

Shut down Registry Editor and then launch Outlook again. The new limit on the size of OST files will now be in effect.

Important Things to Think About When Making OST Bigger

Increasing the size of the OST can help you store more data, but you need to make sure that the system works well and that the data stays safe.

Don't establish size limitations that are too large, as this could make Outlook run slower.

Archive old emails on a regular basis to keep the file size manageable.

Keep an eye on the synchronization status to make sure it doesn't get messed up.

Method 2: Instead of making the OST file bigger, make it smaller.

Sometimes, making the OST file bigger isn't the best thing to do. Instead, users can use Outlook's built-in tools to make their OST files smaller.

Put Old Emails in an Archive

Outlook has an archive option that puts old emails into a different PST file. This makes the OST file load less and speeds things up.

Conclusion

OST files are very important for letting you access Outlook data when you're not connected to the internet. But hitting the default file size restriction can slow both work and email syncing.