Looking for a trivial mail relay in docker
reddit / selfhosted

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kalsan15 · 2023-12-12 15:44

Hi! When I've started my research into this several hours earlier, I
was under the impression that what I'm looking for is straightforward,
trivial and an absolute mainstream use case. Hours of pointless
research have made me doubt that, or, perhaps even more true, my very
own sanity.

This is what I'd need: Given a set of machines that are part of the
same LAN, I want to spawn a docker container providing an SMTP relay
without credentials, only available within that LAN. When a machine in
the LAN needs to send a mail (e.g. a failing cronjob etc.), that relay
accepts the message and forwards it to an actual mail server (e.g.
gmail) in the internet, providing credentials. This way, the cronjob
does not have to store and credentials and neither does that host.
SMTP credentials for the true mail server are only stored in the
relay, and if those are to change, I only need to update the config of
a single machine. Also, since it's only in an isolated LAN, I'm not
worried about abuse of the relay.

What I've looked at so far:

* Postfix with SASL but it's insanely complex, there's no docker image
available and I need to update it by rebuilding the image. Also, it's
completely overkill.
* ssmtp or msmtp, but again, there's no docker image available
* Tons of tinker projects such as [https://hub.docker.com/r/philoles/s
smtp](https://hub.docker.com/r/philoles/ssmtp) which claim to provide
exactly what I need (the given example is especially tempting as a
.env file should do the trick), but most of them are unmaintained,
undocumented, or both.
* Gists, Medium articles and tutorials of questionnable quality,
fixing and patching things with ducktape and using outdated software.

I can't believe there's not a single mainstream docker image out there
doing that simple relay magic without the need of compiling, building,
reconfiguring, patching or otherwise doing dirty business. I can't be
the only one facing this, and all config could be done through ENV
variables like so many other docker images do.

I conclude that my research must have been poor and that I've most
likely wasted time searching the wrong thing. So please consider this
to by my public cry for help in this surprisingly hairy topic. What
are the proper terms for what I'm looking for? What are popular
options to solve this?

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thekrautboy · 2023-12-12 15:49

msmtpd by crazy-max

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ripnetuk · 2023-12-12 17:54

I use image: namshi/smtp
It works well relaying via Gmail for me

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CatoDomine · 2023-12-12 19:31

I did this manually with exim on debian, but anything running an SMTP
server should be able to relay through a "smarthost"

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adamshand · 2023-12-12 20:59

```
❯ cat docker-compose.yml
---
version: "3"
services:
  postfix:
    image: juanluisbaptiste/postfix:latest
    container_name: postfix
    restart: unless-stopped
    ports:
      - "25:25"
    volumes:
      - /etc/localtime:/etc/localtime:ro
    env_file:
      - .env
    environment:
      - DEBUG=no
      - SERVER_HOSTNAME=nikau.example.nz

❯ cat .env
SMTP_SERVER=smtp.gmail.com
SMTP_PORT=587
SMTP_USERNAME=adamshand
SMTP_PASSWORD=lakdsjfalskdfja
```

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HoustonBOFH · 2023-12-12 21:12

I do not have an answer for you, but wanted to compliment you on an
amazingly good question!  You stated what you needed clearly.  You
mentioned what you tried and why it did not meet your needs.  You even
talked about how you looked!  I need to keep this an an example of a
good questions as opposed to "My stuf no work HeLpMe!"

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jakesomething · 2023-12-12 22:31

Check out mailhog

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degan6 · 2023-12-13 05:44

[Mailrise](https://github.com/YoRyan/mailrise) was made to solve this
problem.

I only recently found it,

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kalsan15 · 2023-12-13 15:51

>juanluisbaptiste/postfix

Damn. 2 minutes in and I got a mail by myself. I guess crazy max is
the end of my mad fury road. Thanks a bunch!