E-mail has become a very useful tool in communicating with colleagues. The most common utilities are those receiving and sending mail. In addition it is convenient to have a way of creating aliases and mailing lists. The most primitive such utility is the program ``mailx''. Nowadays, most people on Unix have access to Elm, Pine or other mailers. All these programs are in the public domain. In addition the GNU Emacs editor has a Mail mode in which one can compose and read and manipulate messages.
From the point of view of the system administrator thre has to be a utility that distributes incoming mail and also send outgoing mail to the appropriate channels. Two common such programs are Smail and Sendmail which can both be found in the public domain.