Fix Microsoft Outlook has reached the maximum file size

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Summary: Outlook stores data it downloads from mail servers in a PST or OST file locally in Windows and the default file size is set at 50GB, although with some simple registry edit tweaks this default max file size limit can be increased to 100GB.

Outlook stores data it downloads from mail servers in a PST or OST file locally in Windows and the default file size is set at 50GB, although with some simple registry edit tweaks this default max file size limit can be increased to 100GB.

When do Maximum File Size Problems in Microsoft Outlook occur?

There are a variety of things that can cause you to get an Outlook popup that complains you cannot send / receive email due to max file size, here are some of the common reasons this might happen:

When you have too much email and have not cleared out your emails for a long time
When you have a mailbox that allows you to store more than 50GB of emails such as an Microsoft 365 Plan2 mailbox that allows 100GB rather than the standard 50GB
When you have access to other shared mailboxes such as a Microsoft shared mailbox but unfortunately the shared mailbox contributes to the PST/OST file size on top of your personal mailbox, so it fills up the local PST/OST file and hits the 50GB limit.