OpenSMTPD
OpenSMTPD is a FREE implementation of the server-side SMTP protocol as defined by RFC 5321, with…
8 Alternatives To OpenSMTPD
Agent
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BulkMTA
BulkMTA is Commercial Mail Server Similar to PowerMTA.
Courier-MTA
The Courier mail transfer agent (MTA) is an integrated mail/groupware server based on open…
Exim
Exim is a message transfer agent (MTA) developed at the University of Cambridge for use on Unix systems connected to the Internet.
Haraka
Open source SMTP server written in Node.js
MailEnable
MailEnable is a Windows based mail server and email server program that is packed with the state of the features and functions like antivirus and spam filtering system, webmail management system, cardDAV, CalDAV and much more.
NikaMail
NikaMail is a portable, extendable, zero-config email server.
PowerMTA
PowerMTA is an industrial-strength software for high-volume email delivery.