daknetworks.com

You have a heavy email account who receives a message:

The message store has reached its maximum size.

All messages are stored in a single file. In the past, this was an PST file. In modern times, this is either an OST file or an NST file.

The size can get too large and this can happen because they receive/send too many messages.

The is can be solved by:

1- manual archive:
If needed, you can archive items older than a certain date:
-OUTLOOK
-click FILE > CLEANUP-TOOLS > ARCHIVE:

2- in-place archive
See article here: http://www.daknetworks.com/blog/445-in-place-archive-exchange-2013

Another contributing factor is SHARED-MAILBOXES as they count towards the OST/NST file size.

There is a manual setting:
-OUTLOOK
-click FILE > ACCOUNT-SETTINGS > ACCOUNT-SETTINGS
-click CHANGE
-click MORE-SETTINGS
-click ADVANCED tab (at the top)
-uncheck DOWNLOAD-SHARED-FOLDERS
-click OK > NEXT > FINISHED

This can also be done by registry edit. Here is a one-liner:

REG ADD "HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\Outlook\Cached Mode" /v "CacheOthersMail" /t REG_DWORD /d 0 /f