There are many ways of obtaining another user's electronic mail address.
For users here at Sydney University, you can send electronic mail only to a user that you already know his/hers e-mail address.
You can also access the University of Sydney Phonebook under the Studnet Information section of the Sydney University Web Server.
To find off-campus users, a few Electronic Mail Search Tools are available and detailed under the lesson Finding People from these on-line course series.
Of course, if an electronic method of finding a user's electronic mail address doesn't work, you can always use other forms of communication (such as the telephone or postal mail) to ask them for their address. Note that many people are also placing their electronic mail address on their business cards.