This works fine on a Digital Ocean droplet LAMP install.
Sendy is an email platform that allows you to send emails via AmazonSES.
It has a feature to use custom domains for tracking clicks etc. You add the custom domain and then it tells you to add it as a CNAME that points to the sendy install.
in general, you can have a zone that looks like this
www in cname something.elsewhere.domain.com.
blog in cname something.elsewhere.domain.com.
on your server you will need valid certificates for www.yourdomain and blog.yourdomain, and itβs irrelevant if you have a valid cert for the cname destination something.elsewhere.domain.com.