[Domain Mapping] All mapped sites return 500 error

All mapped subdomain sites are returning a 500 error when using WPMU DEV Domain Mapping plugin.
Because we use external mail server, we need to use CNAME for the www version of each mapped domain, and point the non-www to www, and cannot point the "A" record to the multisite IP.
This setup was working fine before when using the old domain maping plugin from wordpress.org, but we can't get things working right with your plugin.