Office 365 - How to check your mailbox quota usage?

You can check most recent quota usage of your Exchange account by using Outlook Web App (OWA) or Microsoft Outlook:

• Outlook Web App (OWA)
• Microsoft Outlook 2010

Outlook Web App

To get your account information such as Mailbox usage:

1. Click Outlook in the Outlook Web App page.
2. Go to the upper right corner and choose Settings  >Options > General -> My account.
3. Mailbox usage is within the my account page.

Outlook 2010

1. In the "Mailbox Cleanup" section, click Cleanup Tools.
2. Select Mailbox Cleanup... from the drop-down list.
3. Click View Mailbox Size....
4. After viewing your mailbox usage, close the pop-up windows.
5. Click the Home tab brings you back to the messages pane.