In google workspace one can define external hosts either by IP adress or by domain.
So in this case I would add the host-name of the cloudon mail sever ( e.g. mail.cloudron.test:587).
The MX record of the domain would point to google.
Now for all email adresses which I would like to keep in cloudron I would add the rerouting option to the cloudron mailsever host.
Note: This already works. I tested it.
The problem is that if I then send a mail from an email-adress hosted at the cloudron instance to email adress hosted on google but on the same domain it runs into delivery problems. I suppose this is because cloudron tries to internally deliver the emails.
So I would hope for an option that disables the internal email routing, so that every email is sent to the sever sepcified in the MX record.
This is why OP asks for the ability to "disable internal routing for emails on certain domains".
This option would really help massively 🙂