Electronic mail, or e-mail, is a fact of life in most working environments. People rely on it for technical discussions (if you have a problem using a system, you can ask an expert and get a response within minutes), sharing data and programs, working on papers with colleagues (mailing new drafts back and forth), and many other reasons. E-mail is fast---data files several thousand bytes long can be sent around the world in seconds---and it is also convenient. If the person you are communicating with is on the other side of the world your message will be waiting for them when they show up for work in the morning.
Since there are so many different mail systems, and often many different interfaces for each one, we will not try to describe any particular system here. Instead, we will just try to convince you to learn one of the e-mail systems on your local network if you have somehow avoided e-mail until now.
In addition to interacting with colleagues, e-mail is a default interface to many of the resources to be described in the section on Internet services. For example, one way to obtain technical reports from a university is to use the file transfer program FTP. If your machine is not on the Internet, FTP will not be able to connect to the remote machine. But machines that are not directly connected to the Internet can send mail to Internet sites, and it may be possible to retrieve a paper by sending e-mail to a server at the university. All you need to do is put the words ``send X'' in the body of your message, and the server will send you a copy of X within a few hours. Many other Internet services also have e-mail interfaces.