courier-base 0.68.2-1ubuntu7 (arm64 binary) in ubuntu xenial

 The Courier mail transfer agent (MTA) is an integrated mail/groupware
 server based on open commodity protocols, such as ESMTP, IMAP, POP3, LDAP,
 SSL, and HTTP. Courier provides ESMTP, IMAP, POP3, webmail, and mailing list
 services within a single, consistent, framework.
 .
 This package provides the functionality needed by all courier packages
 such as some configuration files, helper programs and the Courier TCP server
 daemon.