Question. Is it possible to use this setup for all settings? I would like to use it for the port and servername aswell

Good spot! You are right, we should add this information in the README.

Really, we should add it because the library not only supports this feature for username and password, it already supports it for all configuration fields.

What do you think of adding a more general sentence in the README about the support of {:system, "ENVIRONMENT_VARIABLE"} and also one in the documentation? 😁

What do you think about that addition to the README

Thanks - looks good to me! 👍

If you can also add this sentence to the library documentation and rebase your commits, we will be really happy to merge it

develop is the default branch on your repository?

rebasing won't do anything, unless I am missunderstanding

Sorry - you are right the default branch is develop. I meant squashing your commits.

There is a squash and merge option on PRs is there not.

That's right, I always forget about this feature :)

Anyway, we can't merge the PR right now because the build fails. Credo found this issue on your last commit:

Code Readability                                                              
┃ 
┃ [R] ↓ There should be no trailing white-space at the end of a line.
┃       lib/bamboo/adapters/smtp_adapter.ex:7:1 (Bamboo.SMTPAdapter)

It's a shame these tools can't make formatting changes. I normally just use the github web interface when contributing to documentation stuff.

Thanks for the Pull Request :)