Installing the command-line executable

Assuming you have Rust/Cargo installed, run this command in a terminal:

cargo install mailsis-smtp

It will make the mailsis-smtp command available in your PATH if you've allowed the PATH to be modified when installing Rust. cargo uninstall mailsis-smtp uninstalls.

Back to the crate overview.

Readme

Mailsis

Simple (yet efficient) SMTP and IMAP server.

Mailsis has been written for educational purposes and shouldn't be taken too seriously. Use it at your own risk!

Description

Built on top of the powerful Rust Programming Language, Mailsis provides a safe and efficient implementation of the classic SMTP and IMAP protocols.

Features

Simple and efficient SMTP server
Powerful IMAP server
Authentication with SASL
Mailbox storage, with support for multiple users
File-system based, allowing for easy integration with existing systems

SMTP Server

Run the SMTP server from the workspace root:

cargo run -p mailsis-smtp

Configuration is loaded from config.toml by default. To point to a different config file, set the MAILSIS_CONFIG environment variable before launching.

By default, the server listens on 127.0.0.1:2525. You can override the bind address with HOST and PORT environment variables.

Authentication uses passwords/example.txt, and smtp.auth_required is false by default. Set it to true in the config to require credentials.

Redis Routing

Mailsis SMTP can route incoming emails to a Redis queue instead of (or in addition to) local file storage. This requires the redis cargo feature and a running Redis instance.

Build with the redis feature:

cargo build -p mailsis-smtp --features redis

Start a Redis server (e.g. via Docker):

docker run -d --name redis -p 6379:6379 redis

Configure config.toml to define a Redis handler and routing rules:

[smtp.handlers.local]
type = "file_storage"
path = "mailbox"
metadata = true

[smtp.handlers.redis_queue]
type = "redis"
url = "redis://127.0.0.1:6379"
queue = "incoming_emails"

[smtp.routing]
default = "local"

# Route all emails for example.com to Redis
[[smtp.routing.rules]]
domain = "example.com"
handler = "redis_queue"

Run the SMTP server:

cargo run -p mailsis-smtp --features redis

Send an email to a routed address and verify it lands in Redis:

redis-cli LRANGE incoming_emails 0 -1

# Or, if Redis is running in Docker:
docker exec redis redis-cli LRANGE incoming_emails 0 -1

Each message is pushed as a JSON object with message_id, from, to, subject, and body fields. See config.example.toml for the full set of routing options (per-address, per-domain, and wildcard domain rules).

IMAP Server

Run the IMAP server from the workspace root:

cargo run -p mailsis-imap

By default, the IMAP server listens on 127.0.0.1:1430. You can override the bind address with HOST and PORT environment variables.

Authentication uses passwords/example.txt and messages are read from mailbox/.

Examples

Note: Start the SMTP/IMAP servers before running the example clients. The example credentials in passwords/example.txt include sender@localhost:password and recipient@localhost:password.

SMTP Python client (sends a test email with an attachment):

python smtp/examples/smtp_client.py

SMTP Rust clients:

cargo run -p mailsis-smtp --example smtp_client

cargo run -p mailsis-smtp --example smtp_raw

The smtp_client example validates TLS using certs/ca.cert.pem. The smtp_raw example can optionally take a file path to send as an attachment.

IMAP Python client (reads the latest email from INBOX):

python imap/examples/imap_client.py

License

Mailsis is currently licensed under the Apache License, Version 2.0.