Let's say I want to start a service where customers get their own subdomain on my domain for email addresses only.
I have an A record for mydomain.com and a CNAME for www.mydomain.com
If I add a wildcard MX record for *.mydomain.com, my understanding is that any email coming to my domain will route to the associated mailserver, except for www because CNAME's cannot overlap with MX records.
So email addresses such as
Should all work correctly.
Will NOT work correctly.
Then, in my SMTP mailserver, I can parse the domain out of the email address, and route the message appropriately. Is there anything wrong with this plan?