Hi, I am trying to figure out how did these companies which provide mass email services (mailchimp, sendgrid, and others) create the email servers from which the users can send emails from their own domains. If we try to make a similar (but a lot smaller thing) with one server, I would say that we would set up a simple Linux server with postfix. However, i am not sure how to allow the users to authenticate their domains (with dkim and spf records). The idea is that each user can send fully authenticated emails from their own domain through our server. I know that there is something with cname records, which the users set for their domains. But how would the dkim keys and reverse name resolution work for these cases?
Maybe someone can give ma a hint on what to check. Thanks