courier-mta-ssl 0.68.2-1ubuntu7 (s390x 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.
 .
 ESMTP over SSL is handled by the regular ESMTP daemon from courier-mta
 in conjunction with the SSL/TLS wrapper supplied by courier-ssl.