libESMTP is an SMTP client library intended for software developers. It manages submission of electronic mail via a preconfigured Mail Transport Agent (MTA) such as Exim or Postfix. libESMTP offloads the developer of the need to handle the complexity of negotiating the SMTP protocol by providing a simple API. Additionally libESMTP transparently handles many SMTP extensions including authentication. This is the original libESMTP software previously hosted on stafford.uklinux.net and managed by
Courier is a mail transfer agent (MTA) and groupware server. It implements IMAP, ESMTP, POP3, LDAP, SSL, HTTP, iCal. It also provides mailing list management, filtering, maildirs storage, and a webmail interface with calendaring and scheduling.