Hi Carla,
Please use the following steps to solve the problem.
- Verify that the logon page for OWA is displayed correctly, and make sure that the user uses the correct URL for OWA: https://outlook.office.com.
- Try using the private mode of the browser to login. Also, try using another browser to check it.
- Contact an Office 365 admin and use the admin account to sign in Exchange Admin Center. Find your mailbox in Recipients > Mailboxes, select Edit. Navigate to Mailbox features, make sure Email Connectivity is enabled and IMAP, POP3, MAPI are enabled.
If the problem still persists, please give us a screenshot of the Mailbox features interface and tell us how many users are affected.
Regards,
Barry