Raven

Raven is a small mail server written in Zig. It currently provides SMTP, IMAP, filesystem-backed storage, tenant-aware routing, and optional TLS.

Features

• SMTP listener with inbound delivery
• IMAP listener with mailbox access
• Filesystem-backed mail storage
• Tenant/domain routing and alias lookup
• Account authentication from local storage
• Optional TLS via OpenSSL
• Graceful shutdown on signal

Requirements

• Zig 0.16
• OpenSSL 3
• macOS build support currently expects Homebrew OpenSSL at /opt/homebrew/opt/openssl@3

Build

zig build
zig build test

Run

zig build run -- \
  --listen-address 127.0.0.1 \
  --listen-port 5882 \
  --imap-port 1143 \
  --hostname localhost \
  --data-dir data

On first run, Raven creates its filesystem layout under --data-dir.

TLS

Generate a short-lived local certificate:

openssl req -x509 -newkey rsa:2048 -nodes \
  -keyout key.pem -out cert.pem -days 1 \
  -subj "/CN=localhost"

Start Raven with TLS enabled:

zig build run -- \
  --listen-address 127.0.0.1 \
  --listen-port 5882 \
  --imap-port 1143 \
  --hostname localhost \
  --data-dir data \
  --tls-cert cert.pem \
  --tls-key key.pem

Connect with openssl s_client:

openssl s_client -connect 127.0.0.1:5882 -quiet -CAfile cert.pem
openssl s_client -connect 127.0.0.1:1143 -quiet -CAfile cert.pem

Configuration

Raven accepts configuration from:

• CLI flags
• Environment variables
• key = value config files

Common options:

• --config
• --listen-address
• --listen-port
• --imap-port
• --hostname
• --data-dir
• --tls-cert
• --tls-key

Environment variables use the RAVEN_ prefix:

• RAVEN_CONFIG
• RAVEN_LISTEN_ADDRESS
• RAVEN_LISTEN_PORT
• RAVEN_IMAP_PORT
• RAVEN_HOSTNAME
• RAVEN_DATA_DIR
• RAVEN_TLS_CERT
• RAVEN_TLS_KEY

Example config file:

listen_address = 127.0.0.1
listen_port = 5882
imap_port = 1143
hostname = localhost
data_dir = data
tls_cert_file = cert.pem
tls_key_file = key.pem

Testing

• zig build test runs the unit test suite.
• For a manual smoke test, connect to the SMTP and IMAP ports and verify the greeting banners.

Architecture

• src/main.zig wires configuration, startup, TLS, and shutdown.
• src/server.zig handles SMTP sessions and inbound delivery.
• src/imap.zig handles mailbox access and IMAP commands.
• src/storage.zig manages the filesystem layout and message files.
• src/config.zig loads CLI, environment, and config-file settings.
• src/tls.zig wraps OpenSSL for server-side TLS.
• src/tenant_index.zig, src/alias_index.zig, and src/account_index.zig provide routing and identity lookup.

Contributing

• Keep changes small and focused.
• Run zig build and zig build test before opening a PR.
• If you touch startup, TLS, or storage behavior, add or update tests.
• Prefer minimal changes that preserve the current architecture.

License

MIT