The Free On-line Dictionary of Computing (30 December 2018):
1. A program that distributes files or
information in response to requests sent via electronic
mail. Examples on the Internet include Almanac and
netlib. Mail servers are also used on Bitnet.
In the days before Internet access was widespread and UUCP
mail links were common, mail servers could be used to provide
remote services which might now be provided via FTP or
2. (Or "mail hub") A computer used to store and/or
forward electronic mail.