Mox

Mox is an open-source, self-hosted mail server designed for low-maintenance email management on custom domains. It functions as a complete mail solution, providing the necessary infrastructure to receive, submit, and deliver email while offering a built-in webmail interface for browser-based access. The software handles the full lifecycle of email communication, from the initial SMTP handshake to the final delivery into a user mailbox.

The software is deployed as a server application on Unix systems, typically running on a dedicated virtual machine to ensure proper network visibility for junk filtering and rate limiting. It includes a web admin interface for managing domains, accounts, and aliases, and can be installed as a system service. For developers and testers, it provides a localserve subcommand that allows for running a local instance of the server to test email-related functionality in a controlled environment.

Key features

• SMTP and IMAP4 support with extensions for email delivery and client access
• Built-in webmail and a web-based administration interface
• SPF, DKIM, and DMARC authentication including aggregate reports
• Bayesian spam filtering and reputation tracking per user
• Automatic TLS certificate management via ACME for Let's Encrypt
• DANE and MTA-STS support for secure inbound and outbound delivery
• Account autodiscovery via SRV records and device management profiles
• HTTP/JSON API for sending transactional emails and receiving webhooks
• Integrated webserver for serving static files and reverse proxying

Written in Go, Mox is designed for users who want to maintain their own email infrastructure without complex configuration. It integrates Prometheus metrics and structured logging for operational monitoring. The architecture includes a built-in webserver to handle ACME challenges on port 443, which can also be used to serve websites on the same machine to avoid port conflicts. The codebase is heavily cross-referenced with RFCs to ensure maintainability and adherence to standards. It is compatible with various email clients, including Mozilla Thunderbird, Microsoft Outlook, and mobile mail apps, and has been tested for interoperability with major cloud providers.

Mox is positioned as a modern, all-in-one mail server for individuals and organizations seeking a self-hosted communication stack.