I’ve been scratching my head over the postfix-relay as you have, until I realized my ISP(running the server at home) blocks port 25.

So I got the SMTP provider approach to work, through Brevo. I’ll detail my steps here. I also tried to setup using gmail but I got an authentication error so I quickly gave up on that.

Sign up to Brevo

Register at Brevo with your totally legit existing company name, then choose the free plan. This allows 300 free emails sent/day.

On the dash page, click in the top right -> “SMTP & API”. Here’s your login information for the lemmy.hjson config. Use the SMTP key value as your smtp_password

Edit your lemmy.hjson

lemmy.hjson

email: {
  # Hostname and port of the smtp server
  smtp_server: "smtp-relay.brevo.com:587"
  # Address to send emails from, eg noreply@your-instance.com
  smtp_from_address: "noreply@example.tld"
  smtp_login: "<brevo login email>"
  smtp_password: "<smtp key>"
  # Whether or not smtp connections should use tls. Can be none, tls, or starttls
  tls_type: "starttls"
}

With this approach you also don’t need postfix-relay in your docker-compose.

With this setup, you should be able to get the verification/password reset emails to be sent. However the recipient will receive a phishing warning or perhaps the email won’t even get through, because your DKIM signature doesn’t match your domain.

DKIM signature

To get a proper DKIM signature, you also need to edit your DNS records.

From the Brevo dashboard click the topright menu again -> “Senders & IP”.

Go to “Senders” and edit the “From email” field to your own domain example.tld

Then go back and go to “Domains” -> “Add a domain”. Add in your example.tld and probably choose “Other” for provider. In the next page you get records to add to your DNS provider. If you don’t know how this works there’s a tutorial linked on that page.

Click authenticate, and you should now see green checkmarks if done correctly :).

Keep in mind you won’t receive emails if someone replies to these, since there’s no IMAP setup.

Do tell if there’s anything wrong with these instructions, I only wrote it from memory.