Delivery error for parent domain

Delivery error for parent domain

Hello,
I have registered Zoho Mail with subdomain.domain.com.
When I try to send an email to domain.com, I get a Mailer Daemon error message:
INVALID_ADDRESS, ERROR_CODE :554, ERROR_CODE :5.7.1 
It looks like if Zoho would not allow email to be routed out to the parent domain.
Any idea what is wrong with my configuration?
Best