SMTP config to use localhost or 172.17.0.1 is not working, how to debug

[meglio (Anton)]

Turns out the traffic needs to be redirected, read more here:

Use Protonmail Bridge with Discourse

Problem: a) Protonmail Bridge cannot listen to IP other than 127.0.0.1, and b) Discourse in a Docker container cannot send SMTP requests to 127.0.0.1 of the host machine. Solution: We configure it to send to 172.17.0.1 (the Docker’s bridge IP on the host machine), and then redirect to 127.0.0.1, on which the Protonmail Bridge is listening. We do it with using Socat. How To Start by installing Socat: apt install socat We will run Socat as a service. Create service file: nano /etc/systemd/sy…