One server for your email, calendars, contacts and shared files, with spam and phishing protection built in. Every standard protocol your clients already speak (JMAP, IMAP, POP3, SMTP, CalDAV, CardDAV and WebDAV) supported natively.

Running mail used to mean stitching together half a dozen separate components (an MTA, a message store, a spam filter, a calendar server, a contacts server, a file server) each with its own configuration quirks. Stalwart collapses all of that into one platform: fewer services to deploy, one configuration to learn, one place to look when something needs attention, and a smaller attack surface.

OPEN SOURCE EMAIL INFRASTRUCTURE for enterprises and high-volume senders

Because KumoMTA is Open Source, we don’t charge for the software — this work is sustained entirely through sponsorships. When you become a sponsor you not only gain access to support and services, you also help power the continued innovation and progress of today’s most advanced email solution.

All prices are per billion messages per year, with no limits on number of servers.

Higher volume senders can contact us for custom pricing.

Mailu is a simple yet full-featured mail server as a set of Docker images. It is free software (both as in free beer and as in free speech), open to suggestions and external contributions. The project aims at providing people with an easily setup, easily maintained and full-featured mail server while not shipping proprietary software nor unrelated features often found in popular groupware.

Main features include:

• Standard email server, IMAP and IMAP+, SMTP and Submission with auto-configuration profiles for clients

• Advanced email features, aliases, domain aliases, custom routing, full-text search of email attachments

• Web access, multiple Webmails and administration interface

• User features, aliases, auto-reply, auto-forward, fetched accounts, managesieve

• Admin features, global admins, announcements, per-domain delegation, quotas

• Security, enforced TLS, DANE, MTA-STS, Letsencrypt!, outgoing DKIM, anti-virus scanner, Snuffleupagus, block malicious attachments

• Antispam, auto-learn, greylisting, DMARC and SPF, anti-spoofing

• Freedom, all FOSS components, no tracker included

Postal is a complete and fully featured mail delivery platform for use by websites & web servers. Think Sendgrid, Mailgun or Postmark but open source and ready for you to run on your own servers.

Mailpit - email & SMTP testing tool with API for developers

Mailpit is a small, fast, low memory, zero-dependency, multi-platform email testing tool & API for developers.

It acts as an SMTP server, provides a modern web interface to view & test captured emails, and contains an API for automated integration testing (read more).

A comprehensive email domain validation library. Supports DNS, MX, SPF, SMTP, DKIM, DMARC, BIMI, TLSRPT and MTA-STS.

MX record validation SMTP server connection testing DKIM record lookup DMARC policy validation MTA-STS support (RFC 8461) IPv4/IPv6 support Local IP blocking DNS failover resolvers Punycode/IDN support TypeScript support