How to check my M365 mailbox usage?
You can check your M365 mailbox quota and usage in the "Options" of Microsoft 365 Outlook Web App (OWA):
- Login your M365 account at
CityU Staff Sign in to Microsoft 365 web page.
- Click gear icon at the top-right corner of OWA window.
- Select Mail under Your app settings.

- Select My account under General. The Mailbox usage of your mailbox will be shown.

Return to FAQs on CityU Microsoft 365
IT.ServiceDesk@cityu.edu.hk