Cost / License
- Free
- Open Source (CC0-1.0)
Application type
Platforms
- Self-Hosted
- Roundcube
United States

Postfix is described as 'Mail transfer agent (MTA) that routes and delivers electronic mail. It attempts to be fast, easy to administer, and secure. The software is also known by its former names VMailer and IBM Secure Mailer' and is a Mail Server in the online services category. There are more than 25 alternatives to Postfix for a variety of platforms, including Linux, Mac, Windows, Self-Hosted and BSD apps. The best Postfix alternative is Mail-in-a-box, which is both free and Open Source. Other great apps like Postfix are Exim, Mailpit, MailHog and Stalwart.

Exim is a message transfer agent (MTA) developed at the University of Cambridge for use on Unix systems connected to the Internet.


Stalwart is an open-core mail server solution with JMAP, IMAP4, POP3, and SMTP support and a wide range of modern features. It is written in Rust and designed to be secure, fast, robust and scalable.

KumoMTA is the only true Open-Source PowerMTA alternative, capable of matching performance of several million messages per hour while providing granular traffic shaping configuration and automation across unlimited IPs.

OpenSMTPD is a FREE implementation of the server-side SMTP protocol as defined by RFC 5321, with some additional standard extensions. It allows ordinary machines to exchange e-mails with other systems speaking the SMTP protocol.
Sendmail is a general purpose internetwork email routing facility that supports many kinds of transfer and delivery methods, including the Simple Mail Transfer Protocol (SMTP) used for email transport over the Internet.

MailDotNull is a local mail catcher for development. It emulates the HTTP send APIs of popular email providers (Resend, SendGrid, Mailjet, Mailgun, Postmark, Brevo, Amazon SES) plus plain SMTP with STARTTLS and SMTPS.



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.