Hi,
Please try exiting Outlook desktop client and see if the issue can be reproduced on the web mail.
In this situation, please start your Outlook in safe mode (Press Win + R, type “outlook /safe”, press Enter.) and see if the issue continues.
This alert may be indicating that your mailbox capacity is insufficient. A big mailbox can cause many complicated problems, so it is sugegsted to reduce the size of your mailbox.
- Archive your messages.
- Reduce the size of your mailbox.
Once you reduce the size of your mailbox, this alert should not pop up anymore.(If you are unable to open Outlook to clean your mailbox, please go to your webmail and delete some old items and see if there is any difference.)
Hope this can be helpful.
Regards,
Aidan Wang
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