Simple SMTP Relay

Application written in Rust that listens for SMTP clients, reads e-mails and then delivers them using Azure Communication Services.

The server has been inspired by the work done by Piotr Sarna.

Installation

You need to install a Rust toolchain with cargo. Please refer to Install Rust for up-to-date instructions for your platform.

Once you have cargo up and running, execute the following command:

$ sudo cargo install --git https://github.com/andyolivares/simple-smtp-relay.git --root /usr/local

This will download, build and install simple-smtp-relay to /usr/local/bin.

Usage

Usage: simple-smtp-relay [OPTIONS] --endpoint <ACS_ENDPOINT> --access-key <ACS_ACCESS_KEY>

Options:
  -a, --address <IP:PORT>            Address to bind to (defaults to 127.0.0.1:25)
  -d, --domain <DOMAIN>              Domain name (defaults to smtp.domain.com)
  -e, --endpoint <ACS_ENDPOINT>      ACS Endpoint (eg. https://<my_acs_account>.unitedstates.communication.azure.com)
  -k, --access-key <ACS_ACCESS_KEY>  ACS Access Key
  -l, --log-level <LOG_LEVEL>        Log level (eg. trace, debug, info, warn, error)
  -h, --help                         Print help
  -V, --version                      Print version

WARNING: Setting the log level to trace could reveal sensitive information. Never set to trace in production.

Configure as systemd Daemon

If you want to use systemd to manage the application as a system daemon, you need to create a systemd service file.

$ sudo editor /etc/systemd/system/ssrelay.service

Then type in the following:

[Unit]
Description=Simple SMTP Relay Server

[Service]
Environment=ACS_ENDPOINT=https://<my_acs_account>.unitedstates.communication.azure.com
Environment=ACS_ACCESS_KEY=<my_access_key>
ExecStart=/usr/local/bin/simple-smtp-relay -e $ACS_ENDPOINT -k $ACS_ACCESS_KEY

[Install]
WantedBy=multi-user.target

Don't forget to replace the right values for ACS_ENDPOINT and ACS_ACCESS_KEY. Once you have the service file in place, reload systemd and start the service. You can add any other option in the ExecStart command line (eg. another address/port to bind to, domain name, log level, etc.).

Everytime you modify the service file, you need to reload systemd:

$ sudo systemctl daemon-reload

Then enable and start the service:

$ sudo systemctl enable ssrelay
$ sudo systemctl start ssrelay
$ sudo systemctl status ssrelay

At this point, you should see the service up and running (STARTED). To see live service logs, you can run:

$ sudo journalctl -u ssrelay -f