Email routing is great, but as it is designed mainly for receiving inbound emails, it is very difficult to use the custom email address as a normal two-way communicating address. Still, I would like to use email routing to do some automation, it would be great if I could still use other provider to send and receive emails with my root domain, and setup email routing for my subdomain(s). It seems that, according to the instruction on dashboard, the subdomain is tied to the root domain and setting it up requires changing the MX records of the root domain.
I am not sure why they have to be tied together, if there is a specific reason, I am happy learn more about it. Thank you!
Surprisingly, the routing rules for the subdomain works perfectly (not sure why).
I guess my problem is solved, but the presentation of the dashboard is kinda confusing in my opinion.