The Free On-line Dictionary of Computing (30 December 2018):

mail server
mail hub

   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
   WWW.

   2.  (Or "mail hub") A computer used to store and/or
   forward electronic mail.

   (1995-05-05)