http://protonmailrmez3lotccipshtkleegetolb73fuirgj7r4o4vfu7ozyd.onion/support/custom-domain-aws
Again, it may take up to a day for MX changes to propagate, and email may still go to your old MX during this transition. Once we detect your domain’s top MX record is pointing to Proton Mail, the MX tab will show a green tick icon.