DNS configuration for users with own subdomains

DNS configuration for users with own subdomains

Hello, I would like to configure my domain to allow each user to use their own subdomains (even on different server) but also have part of email address before @ as their username without subdomain behind. Example:

Hosted on ZOHO:
user1@domain.com
work@user1.domain.com
noreply@user1.domain.com

But I dont want to limit users from using different email providers, so I am not sure, if it is correct to set MX record at DNS for the whole domain.com to ZOHO servers.

How to correctly setup DNS and ZOHO to allow above configuration, but also allow following:

Hosted somewhere else:

Thank you in advance!