arcline-email

A self-hosted mail server written in Go. Handles inbound and outbound SMTP, IMAP access, DKIM signing, and SPF/DMARC verification — no third-party relay required.

Status

Early development. Not production-ready.

Goals

Full SMTP server (inbound on port 25, submission on 587/465)
IMAP server (143/993) for client access
Maildir-based message storage
Username/password authentication with SASL
TLS on all listeners (Let's Encrypt or bring-your-own cert)
DKIM signing for outbound mail
SPF and DMARC verification for inbound mail
Outbound routing via MX DNS lookup
Admin API for managing domains, mailboxes, and aliases

Non-Goals (for now)

Webmail UI
Anti-spam scoring engine (may integrate rspamd via milter later)
Multi-server clustering

Tech Stack

Language: Go 1.22+
SMTP: emersion/go-smtp
IMAP: emersion/go-imap
Mail parsing: emersion/go-message
SASL: emersion/go-sasl
Storage: Maildir (filesystem)
Config: TOML

Project Layout

arcline-email/
├── cmd/
│   └── arcline-email/   — main entry point
├── internal/
│   ├── smtp/            — SMTP server (inbound + submission)
│   ├── imap/            — IMAP server
│   ├── storage/         — Maildir storage layer
│   ├── auth/            — user authentication
│   ├── dkim/            — DKIM signing and verification
│   ├── spf/             — SPF checking
│   ├── dmarc/           — DMARC policy enforcement
│   └── admin/           — admin API
├── config/              — config parsing and validation
├── docs/                — protocol notes, architecture docs
├── todo.md
├── CONTRIBUTING.md
├── LICENSE
└── README.md

Building

go build ./cmd/arcline-email

Running

./arcline-email --config /etc/arcline-email/config.toml

Configuration

See docs/config.md (coming soon).

License

MIT. See LICENSE.

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