How to Increase Outlook Mailbox Size on PC or Mac

Last Updated: July 5, 2023

This wikiHow teaches you how to increase the size of your Microsoft Outlook mailbox by editing the Windows registry. There is no way to increase the mailbox size in Outlook for macOS.

Things You Should Know

There is no way to increase the mailbox size in Outlook for macOS.
In Windows, edit the registry to increase the size of the Microsoft Outlook mailbox.
Press "Win + R" and enter "Regedit" to open the Registry Editor.

Steps

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This opens the Run tool.
A confirmation message will appear, asking if you want to allow the app to run.

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The regedit window will appear.
It’s in the left column. Several options will expand below.
You may have to scroll down a little to see it. A list of software manufacturers will appear.
A list of Microsoft products will appear in the right column.
Instead of “(version)” you will see the version of Office you’re using (2016, 2013, etc).
Do this somewhere under the “Default” line that’s at the top of the panel. A context menu will expand.
Another context menu will expand.
Select the option that reflects your version of Windows.
You have now created a registry key called MaxLargeFileSize. Now you’ll create another.
This new key will appear below the one you created a moment ago.
A dialog will appear.
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Enter the desired size of your mailbox in MB. Type it into the “Value data” field. ^{[1]
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- For example, to make your mailbox 75 GB, type 75000 into the box.
- The default mailbox size for Outlook 2013 or 2016 is 50 GB. The default for Outlook 2003, 2007, and 2010 is 20 GB.
Now you’ll do something similar for the next key.
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Enter the size at which you want to be notified that the mailbox is almost full. Again, enter this in MB.
- For example, if you’ve made your mailbox 75000 MB, you may want Outlook to warn you that you’re nearing the limit at 72000 MB.
You have now updated the registry to support a larger mailbox in Outlook.
Changes to the registry will not take effect until you’ve restarted Windows.