Self-Hosted Email Server Stacks

Mailu is a complete email distribution system deployed as a suite of containerized images. It provides a self-hosted email infrastructure that integrates a webmail client interface with a centralized administration dashboard for managing domains, user accounts, and storage quotas. The system focuses on email deliverability and security through a framework that implements identity verification records and digital certificates. This includes the use of identity signatures and encryption to secure mail transport and prevent domain spoofing. The platform includes layered spam and malware filtering using greylisting and auto-learning engines. It further manages email traffic through rule-based routing, aliases, and user-level configurations for automated responses and server-side filtering.

Mail-in-a-Box is a self-hosted email server appliance that automates the deployment of SMTP, IMAP, and POP3 services on Linux. It functions as a complete suite including a DNS management server, a spam and abuse filter, and a web-based administrative control panel for managing users, aliases, and storage quotas. The project distinguishes itself through a high degree of automation for email security and authenticity. It automatically provisions and maintains SPF, DKIM, DMARC, and DNSSEC records to prevent domain spoofing, while managing the installation and rotation of TLS certificates and enforcing secure transport policies like DANE and MTA-STS. The system includes integrated tools for server health monitoring, network-level brute-force mitigation, and policy-driven spam filtering using greylisting and IP blacklists. It also provides data management capabilities such as system backups to S3-compatible object storage and the ability to serve static website content over HTTPS.

Postal is an open-source email infrastructure and self-hosted delivery platform. It functions as an SMTP mail server and inbound email gateway, providing the tools necessary to send and receive email through a privately managed infrastructure. The system manages SMTP infrastructure for outgoing message delivery and provides capabilities for custom email receiving. It allows for the routing of incoming external emails to internal applications or websites for automated processing. The platform includes support for multi-tenant domain mapping, event-driven webhook notifications, and plugin-based message filtering. It also incorporates queue-based delivery retries and DNS-based recipient validation to manage mail flow and server reputations.

Stalwart is a self-hosted email and collaboration infrastructure that provides an integrated mail server supporting SMTP, IMAP, POP3, and JMAP protocols. It functions as a comprehensive communication hub, combining email hosting with a collaboration server for shared calendars, contacts, and files. The system distinguishes itself through a distributed architecture that uses peer-to-peer cluster coordination to ensure high availability and fault tolerance. It features a built-in security suite that implements an S/MIME and OpenPGP email gateway alongside automated TLS certificate provisioning via the ACME protocol. The platform covers a broad range of capabilities, including multi-layer sender authentication, scriptable mail routing through Sieve and regular expressions, and full-text content indexing. It also provides identity and access management through support for LDAP, SQL, OIDC, and OAuth, while offering administrative tools such as a web dashboard and automated DNS record management. System health is monitored via Prometheus and OpenTelemetry, and the server supports pluggable storage backends including S3-compatible blob storage.

This project provides a full-stack, containerized mail server platform designed for self-hosting. It functions as a complete mail transfer agent that bundles essential services—including SMTP, IMAP, and POP3—into a unified environment. By leveraging container orchestration, it enables the deployment of private email infrastructure that handles message transport, delivery, and user management within a single, manageable service. The platform distinguishes itself through deep integration with container runtimes and robust configuration flexibility. It supports granular customization via configuration-file injection, initialization-script hooking, and volume-based persistence, allowing administrators to tune mail transport parameters and maintain state across container lifecycles. It also offers advanced operational capabilities such as multi-tenant relay routing, automated container updates, and native support for Kubernetes environments. Beyond core delivery, the server includes a comprehensive security and filtering suite. It integrates modular middleware for real-time spam and malware analysis, enforces cryptographic signing for message authenticity, and provides automated protection against brute-force attacks and malicious traffic. Administrative tasks are simplified through a dedicated command-line utility for account management, alias configuration, and storage quota enforcement, alongside built-in observability tools for monitoring server health and filtering statistics. The project is distributed as a container image, with documentation and configuration patterns provided to support deployment across standard container runtimes and orchestration platforms.

Maddy is a modular mail server that assembles a complete email system by connecting small, single-purpose modules through a declarative configuration file. Rather than a monolithic stack, it lets operators compose message processing, storage, authentication, and security enforcement from interchangeable building blocks, with each module handling a specific function like receiving SMTP connections, verifying credentials, or applying policy checks. The server distinguishes itself through its flexible authentication and security architecture. It delegates user verification to external systems including Dovecot, LDAP, PAM, SQL databases, and remote IMAP servers via the SASL framework, while also supporting local password files and SQL-backed credential stores. Security enforcement is comprehensive, applying DKIM, SPF, DMARC, DANE, and MTA-STS checks to both inbound and outbound messages, with configurable actions for policy violations. TLS certificate management is fully automated through the ACME protocol, supporting DNS-01 challenges for domain validation without exposing a public HTTP endpoint. Message handling follows a pipeline model where each incoming message passes through a configurable sequence of checks and delivery steps, with exit codes mapping to actions like accept, reject, or quarantine. Storage backends support SQLite, PostgreSQL, or CockroachDB for IMAP indexes and metadata, while message bodies can be stored in a filesystem or blob store with optional LZ4 or Zstd compression. The server handles multi-domain mailbox management with options for shared credentials, domain isolation, or unified mailboxes, and supports IMAP access with standard extensions including IDLE and MOVE. Deployment options include Docker containers, prebuilt binaries, source compilation, and tarball installations, with DNS record publication for MX, SPF, DKIM, and DMARC. The server exposes an OpenMetrics endpoint for monitoring and supports integration with external tools like rspamd for spam filtering and milter-based mail filters.