Most CAs accept an email to an predetermined address at the domain, which validates that a DNS entry (MX record) on the domain points to a server controlled by the requester.
Many also offer the same thing as Let's Encrypt, which basically verifies if the A/AAAA record for the domain points to a server controlled by the requester.
What am I missing?
Most SSL cert CA's check DNS for email addresses and only validate DNS entries.
Lets Encrypt only checks DNS for IP addresses and issues certs based on root access to the IP addresses.
A CA DV is not equivalent to a Lets Encrypt cert.