OWA 2003 - Log on to other user's mailbox

I needed to log onto one of my client's mailboxes but didn't have access to Outlook at the time.

To access another users mailbox via OWA 2003 (the functionality is built into 2007), log on to OWA as the user with permissions to the other user's mailbox, then change the URL to https://owa.mydomain.com/exchange/useralias/inbox, where useralias is the Exchange alias of the user whose mailbox you wish to access.

Easy!