mailrelay

mailrelay is a simple mail relay that can take unauthenticated SMTP emails (e.g. over port 25) and relay them to authenticated, TLS-enabled SMTP servers. Plus it's easy to configure.

Use case

Some older appliances such as scanners, multi-function printers, RAID cards or NAS boxes with monitoring, can only send email without any authentication or encryption over port 25. mailrelay can send those emails to your Gmail, Fastmail or other provider.

Run mailrelay on a local PC and set your device (e.g. scanner) to send mail to that PC.

mailrelay is written in Go, and can be compiled for any Go supported platform including Linux, MacOS, Windows.

Example (Linux)

On local PC (192.168.1.54) create file /etc/mailrelay.json with contents:

/etc/mailrelay.json

{
    "smtp_server":   "smtp.fastmail.com",
    "smtp_port":     465,
    "smtp_username": "username@fastmail.com",
    "smtp_password": "secretAppPassword",
    "local_listen_ip": "0.0.0.0",
    "local_listen_port": 2525,
    "allowed_hosts": ["*"]
}

Run mailrelay,

./mailrelay

Default location for configuration file is /etc/mailrelay.json but can be changed via --config flag. For example,

mailrelay --config=/home/myname/mailrelay.json

Configure your scanner or other device to send SMTP mail to server 192.168.1.54:2525. Each email will be relayed to smtp.fastmail.com using the credentials above, including any file attachments.

Example 2 (Linux - Systemd service)

Create configuration file as above, and also create,

/etc/systemd/system/mailrelay.service

[Unit]
Description=Mail Relay Service
After=network.target
StartLimitIntervalSec=0

[Service]
Type=simple
Restart=always
RestartSec=5
ExecStart=/usr/local/bin/mailrelay

[Install]
WantedBy=multi-user.target

Copy mailrelay to /usr/local/bin/.

Run,

sudo systemctl start mailrelay
sudo systemctl enable mailrelay

Now mailrelay runs as a service daemon and will automatically start after reboot.

Example 3 (Docker)

edit mailrelay.json as needed then build container and run it

docker build  -t mailrelay .
docker run -v $PWD/mailrelay.json:/etc/mailrelay.json mailrelay

Feedback

Send any questions or comments to wiggin77@warpmail.net