Hello. This is just a suggestion (so free free to ignore it):
Increasingly people seem to want to use Gmail MX or Outlook MX with their domains.
For that to work properly, I need to uncheck "Emaildomain" of course (otherwise any sending email accounts on the local server won't find the target domain's accounts on the MX servers, since the domain gets resolved locally and it tells it there is no such mail box).
In case Froxlor is ported to OpenDKIM, I'd like to suggest of thinking of this possibility from a DKIM perspective, since currently when you turn off "Emaildomain" then of