It is traightforward to send electronic mail between users of different computer systems which are connected to major networks. Most major academic and research institutions and companies throughout the world can now be reached by electronic mail. In addition, a growing number of individuals can be contacted in this way. This is effectively part of the Internet, so email can be exchanged with most national and international networks. All email systems have the ability to send, receive and discard mail.
Most systems have facilities for storing mail which is to be kept rather than discarded.
Mailboxes can soon accumulate a large number of mail messages making it difficult to read and process new mail, in addition to wasting disk space. There is almost always a connection between the email system and the computer's standard file system which allows mail to be read from files or written to files. This enables greater flexibility in how the mail system is used. For example, a mail message may be prepared in a normal file using a familiar text editor and then sent by the email system. Sections of other files may be included in the mail message as well.