generate subdomain email-related DNS automatically

Please enable the zone file generation for using email with a subdomain.

Right now we have to manually contact support and ask for a DKIM and pro-actively set the correct mailserver and SPF TXT records to enable email for a subdomain. It never just works out of the box and there's no alert/notification that these records still need to be added. It could be an automatic process and support are not always 100% on top of this either.