Access USM Webmail (Office 365)
To authenticate with Office 365, enter your e-mail address and password.

Access USM Webmail (On-Premise Exchange)
To authenticate with On-Premise Exchange, enter your username and password.

If you're on a shared or public computer, please remember to log out of your account and close all browser windows when you are done.

Other useful links

What is the new Clutter folder in my mailbox?
How do I manage the USM hosted mailing lists?