1. Login to the Admin Overview page of the Office 365 Portal. Click Manage under SharePoint.
2. Click Manage User Profiles.
3. Click Manage User Profiles under the People heading.
4. In the Find profiles text box, enter the name of the user and click Find.
5. The users matching the search will be displayed. Click the drop-down arrow to the right of the user to edit and click Edit My Profile.
6. Scroll to Work e-Mail and add the user's e-mail address. Save and close when finished. (It will take up to 24 hours to synchronize to the servers.)