Registry Editor

Microsoft Outlook: Dealing with Maximum Message Store errors

UPDATE: A recent update to Microsoft Outlook appears to have changed these instructions some. Look below for updated information.

Upon occassion, I run into errors with some of my clients with regards to their Microsoft Outlook message store. The Outlook message store is a size limit on how big your .pst or .ost file can get in Microsoft. Once it hits that limit, you will receive errors and be unable to retrieve new mail.

Fortunately, though, the limit of the message store is pretty big, so it isn’t a common issue. Here’s a list of the message store defaults for various versions of Outlook:

The good news is that if you have a client that is pushing the envelope with regards to the size of their message store, you can increase these levels using the Windows Registry Editor.

Windows Registry Editor

• Search for regedit.msc; this is the application that loads the Registry Editor.
• Go to HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\xx.0\Outlook\PST (the xx will be a numerical representation depending on the version of Outlook you are running. For Outlook 2016, it will be 16.0)
• UPDATE: The registry key location is now “HKEY_CURRENT_USER\Software\Microsoft\Office\xx.0\Outlook\PST” – the same numerical representation applies (xx will be replaced with the version of Outlook, so for this example, it would be 16.0)
• Look for MaxFileSize and WarnMaxFileSize in registry entries. If you don’t see them, make new D-Word entries and name them the names listed. No spaces, make sure capitalization is correct.
• UPDATE: The Key entries have changed as well. Instead of MaxFileSize and WarnMaxFileSize, they are now MaxLargeFileSize and WarnLargeFileSize.
• Once you make them, double-click on the MaxLargeFileSize to open up the window to modify it. Click on Decimal, and type 102400 (to set the message store to 100GB). Then click OK
• For WarnLargeFileSize, do the same thing but set it to something like 97280, then click OK. The 97280 number represents 95% of the MaxLargeFileSize amount.

Once you have done these things, close out Registry Editor and load up Outlook to see if it takes care of it for you.