Continuing the discussion from How to set SMTP config to use localhost?: [image]How to set SMTP config to use localhost? Just to document here, the following was sufficient (all other SMTP lines commented out) to deliver to the docker host’s smtp server if no auth is necessary: DISCOURSE_SMTP_ADDRESS: 172.17.0.1 DISCOURSE_SMTP_PORT: 25 I’m trying to connect to Protonmail Bridge running at the host machine, and it fails with connection refused. My settings are: DISCOURSE_SMTP_ADDRESS: 172.17.0.1 DISCOURSE_SMTP_PORT: 1025 Now, nmap tests: nmap 127.0.0.1 on the host machine outputs: Nmap scan report for localhost (127.0.0.1) Host is up (0.000010s latency). Not shown: 997 closed ports PORT STATE SERVICE 22/tcp open ssh 1025/tcp open NFS-or-IIS 1042/tcp open afrog nmap 172.17.0.1 in the docker container does not output any 1025 port I also tried in my app.yml file, in expose section: 172.17.0.1:1025:1025 But then the docker container failed to start erroring “the port is already in use”. Finally, if I try to connect with using openssl from localhost: openssl s_client -connect 127.0.01:1025 -starttls smtp it works fine; but not when I try to from the docker container: openssl s_client -connect 172.17.0.1:1025 -starttls smtp Checking with ss on host machine: ss -plnt State Recv-Q Send-Q Local Address:Port Peer Address:Port Process LISTEN 0 4096 127.0.0.1:1025 0.0.0.0:* users:(("proton-bridge",pid=953,fd=12)) What am I doing wrong? One thing I found in this stackoverflow answer says: you will only be able to access host services that are either (a) listening on INADDR_ANY (aka 0.0.0.0) or that are explicitly listening on the docker0 interface. Firstly, I checked iptables --list, which I believe gives default output: iptables --list Chain INPUT (policy ACCEPT) target prot opt source destination Chain FORWARD (policy DROP) target prot opt source destination DOCKER-USER all -- anywhere anywhere DOCKER-ISOLATION-STAGE-1 all -- anywhere anywhere ACCEPT all -- anywhere anywhere ctstate RELATED,ESTABLISHED DOCKER all -- anywhere anywhere ACCEPT all -- anywhere anywhere ACCEPT all -- anywhere anywhere Chain OUTPUT (policy ACCEPT) target prot opt source destination Chain DOCKER (1 references) target prot opt source destination ACCEPT tcp -- anywhere 172.17.0.2 tcp dpt:https ACCEPT tcp -- anywhere 172.17.0.2 tcp dpt:http Chain DOCKER-ISOLATION-STAGE-1 (1 references) target prot opt source destination DOCKER-ISOLATION-STAGE-2 all -- anywhere anywhere RETURN all -- anywhere anywhere Chain DOCKER-ISOLATION-STAGE-2 (1 references) target prot opt source destination DROP all -- anywhere anywhere RETURN all -- anywhere anywhere Chain DOCKER-USER (1 references) target prot opt source destination RETURN all -- anywhere anywhere Now, I’m wondering if the Protonmail Bridge service that’s listening on 127.0.0.1:1025 is not accepting connections from the Docker container because they are not from 127.0.0.1 exactly?

Turns out the traffic needs to be redirected, read more here: [image] Use Protonmail Bridge with Discourse Sysadmins 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…

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

Product Support

meglio (Anton) June 9, 2022, 10:49am 2

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

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

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