Tips for Dealing with Very Large Mailboxes
(This document references the M365 version of Outlook for Windows)
Some users and groups need to have very large mailboxes or otherwise can't delete certain types of email, for historical reference or regulatory reasons.
Background:
- MS 365 Outlook has a hard limit on the size of a mailbox - 100GB. This is a global setting from Microsoft and can't be changed.
- There is the option to get an additional 100GB through what's called an Online Archive, which is configurable by IT. However, this online archive is not searchable by default, when you search Outlook for a really old email. (The Online Archive is searchable separately, however, by selecting the Online Archive and searching there.)
- By default, Outlook on a Windows PC is not configured to handled mailboxes of this size - because very large mailboxes often have performance or stability problems. Below is information on how to allow the maximum amount of data on your Windows PC.
I'm getting an error that Outlook is out of space. What should I do?
Things to check:
1- Is there enough free space on your computer's hard drive? Click the File Folder icon on the task bar below, then click on This PC. Make sure your C drive is not running low on space.
2 - Is my Outlook configured for very large mailboxes? Find and double-click on X:\Public\Apps\2016 Increase OST-PST 100GB.reg file. You'll need to close & reopen Outlook and see if the error goes away.
I still have the problem! Now I'm getting an email that says I'm near the 99GB limit!
This means your primary mailbox is almost full. If you can't delete old email, contact IT and we'll make sure you get setup with an Online Archive.
Once your Online Archive appears in the left side menu, you can either:
1. have IT set up your mailbox for Auto-Archiving, where anything older than 2 years (or 1 year or 6 months) is automatically moved to the Online Archive
2. If you prefer, you can create folders in the Online Archive then drag-and-drop / Move messages from your primary mailbox into the Online Archive until enough space is cleared for the warning emails to stop.
