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. lt is important to discard mail which does not need to be kept, as it uses storage space on disks. 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.
Most systems have a reply facility, although some of these do not always work as expected. Care should be taken when using this facility in electronic mail, as replies do not always go back to the sender.