SMTP to Gotify Docker

This is a simple docker container that forwards SMTP messages to Gotify. I created this so that I could capture emails from applications and appliances that only know how to send emails, but still get notifications in gotify. It's a lightweight server, and the only security considation is that it requires an API Key to authenticate. Use at your own risk, keep this firewalled, etc.

Environment Variables

Variable	Description	Default
GOTIFY_URL	The URL of your Gotify instance
GOTIFY_TOKEN	The token of your Gotify instance
API_KEY	The API key to use for SMTP authentication. This ignores the username value, and only checks the key. This is so that you can have multiple systems report to the same application in Gotify and differentiate them in the notifications. You can use any value you want here, but your email clients will need to use that value as the password.
BIND_IP	The IP address to bind to	0.0.0.0
PORT	The port to bind to	2525
TLS_KEY_PATH	Optional. Path to a private key file used for STARTTLS. If set together with TLS_CERT_PATH, the server will advertise STARTTLS and use this key.
TLS_CERT_PATH	Optional. Path to a certificate file used for STARTTLS. The certificate should match the hostname clients use to connect.

Running

You can run this in many ways, but the point here was having a docker image. I have this deployed in my kubernetes environment alongside my gotify instance.

Here's how you can run it locally with docker:

docker run \
    -p 2525:2525 \
    -e GOTIFY_URL=https://gotify.example.com \
    -e GOTIFY_TOKEN=your-token \
    -e API_KEY=some-secret-you-control \
    imoshtokill/smtp-to-gotify-docker:latest

After it's running, you can test it by sending it a test email. A simple way of testing this is via curl:

curl --url "smtp://127.0.0.1:2525" \
  --user "api_user:some-secret-you-control" \
  --mail-from "[email protected]" \
  --mail-rcpt "[email protected]" \
  --upload-file email.txt \ # where email.txt is a file with the email contents
  --insecure \
  --ssl-reqd

Another way of testing, if you have NodeJS installed, is by running the following in a new, empty directory:

npm init
npm i -S nodemailer

Then create a file called index.js with the following contents:

const { createTransport } = require('nodemailer');

const transporter = createTransport({
    host: "127.0.0.1",
    port: 2525,
    auth: {
        type: 'OAuth2',
        user: 'api_user',
        accessToken: 'some-secret-you-control',
    },
    tls: {
        rejectUnauthorized: false
    }
});

const mailOptions = {
    from: '[email protected]',
    to: '[email protected]',
    subject: `Your subject`,
    text: `Your text content`
};

transporter.sendMail(mailOptions, function(error, info){
    if (error) {
        console.log(error);
    } else {
        console.log('Email sent: ' + info.response);
    }
});

Then run node index.js and you should see the email show up in your gotify instance. If you don't, check the logs of the docker container to see what's going on.

TLS and STARTTLS

This server supports STARTTLS when both TLS_KEY_PATH and TLS_CERT_PATH are set. The files are read from the container filesystem and passed to the SMTP server so that clients such as Alertmanager can require TLS and validate the certificate. In Kubernetes you can mount a cert manager managed secret into the container and point these variables at /certs/tls.key and /certs/tls.crt.