Self-hostable software: Communication - Email - Mail Transfer Agents

MailCatcher
Deploy a simply SMTP MTA gateway that accepts all mail and displays in web interface. Useful for debugging or development.
DetailsHaraka
Fast, highly extensible, and event driven SMTP server.
DetailsOpenTrashmail
Complete trashmail solution that exposes an SMTP server and has a web interface to manage received emails. Works with multiple and wildcard domains and is fully file based (no database needed). Includes RSS feeds and JSON API.
DetailsStalwart SMTP
Modern SMTP server designed with a focus on security, speed, and extensive configurability.
Details
DragonFly
A small MTA for home and office use. Works on Linux and FreeBSD.
DetailsSlimta

chasquid
SMTP (email) server with a focus on simplicity, security, and ease of operation.
Details
Courier MTA
Fast, scalable, enterprise mail/groupware server providing ESMTP, IMAP, POP3, webmail, mailing list, basic web-based calendaring and scheduling services.
Details
EmailRelay
A small and easy to configure SMTP and POP3 server for Windows and Linux.
Details
Exim
Message transfer agent (MTA) developed at the University of Cambridge.
Details
OpenSMTPD
Secure SMTP server implementation from the OpenBSD project.
Details
Postfix
Fast, easy to administer, and secure Sendmail replacement.
Details