Thank you @bilak!

My questions:

• does it work with multi-domains because I see a domainname ENV added to the project.
• I'm not a DKIM expert but is there a way to add integration tests?

Thank you.

• It's now working only for one domain. We can try to convert it to multi-domain in future, but there must be something with what we can decide there's more domains (maybe domainname values separated by comma)
• About integration tests - only thing which we can check is information in log mail opendkim[579]: 359D4A1245: DKIM-Signature field added (s=mail, d=domain.com). I don't know much about postfix neither about docker so your help will be needed.

• You probably don't have to provide a domain list since it already exists and is parsed to create users, aliases and postfix configuration. https://github.com/tomav/docker-mailserver/blob/master/start-mailserver.sh#L20
• For the tests, I will do it, no problem.

• So if I understand it correctly, there could be function created from my script which will accept only domain name (think about how to check duplicated processing - for example ten users with same domain and another 10 users with another domain). There's need to create (if not exists) DKIM (privatet, txt), add entry to KeyTab and to SigningTable.

The postfix/vhost file is generated by startup script and contains unique domains.
I think you can use this file as reference and paste your DKIM startup lines after its generation.

The point is, for these domains, enable DKIM if necessary information are provided.

Thank you @bilak