rmail

Overview

rmail is a self-contained mail server implemented entirely in Python 3 standard library. It handles inbound and outbound email via SMTP, exposes mailboxes over IMAP4rev1, delivers messages to external domains through direct MX resolution or a configured smarthost, and provides a REST/JSON Exchange-style API for programmatic access.

There are no third-party dependencies. Storage is shard-based, using the filesystem with metadata encoded in filenames for lock-free flag operations and atomic updates under concurrent access.

Highlights

• Full SMTP stack — EHLO, AUTH PLAIN/LOGIN, STARTTLS, SMTPS, SIZE enforcement, FROM spoofing detection, per-IP rate limiting
• Outbound relay — authenticated users send to any domain; direct MX delivery (raw DNS UDP) or smarthost; retry schedule up to ~37.5h; DSN bounce generation
• IMAP4rev1 — SELECT, EXAMINE, FETCH, STORE, COPY, MOVE, SEARCH, APPEND, EXPUNGE, IDLE, NAMESPACE, ID, ENABLE, UNSELECT, LITERAL+, SPECIAL-USE
• Exchange HTTP API — stateless JWT authentication, folder and message management, alias management, Thunderbird autoconfig and Exchange autodiscover
• Shard-based storage — lock-free flag changes via os.rename(), fcntl.flock() only for UID allocation, O(1) message operations
• TLS everywhere — auto-generated self-signed certificate on first start, STARTTLS and implicit TLS on all ports, AUTH hidden on cleartext connections
• Zero dependencies — pure Python 3.8+ stdlib, runs on any POSIX system with no package installation
• Aliases and catch-all — per-domain regex rules, exact-match priority, Postfix-style resolution order
• Diagnostics — 8-phase diagnostic suite covering all server components end-to-end

Documentation

Service Ports