Hi,
Well... thank you ZhankHuangbin! You solved the problem with that last sentence. I did not add the service to the domain!
This is so simple and yet, sometimes I don't even think about it!
Also, the command successfully gives the domain 'domain.com' back! So I assume the query works well.
I know this should be obvious that whenever you want to add a functionality to the mail server, the service should be enabled too. But could you add the "enabledService=domainalias" part in your docs on that page :
https://docs.iredmail.org/ldap.add.alias.domain.html
Thank you again!