Placing that up is immensely complex, and jogging it will most likely decelerate your DNS queries, but should you be a veteran with the Linux command-line, take a look at Cloudflare's Directions for DNS around HTTPS and DNS over TLS. The ultimate way to clarify how SMTP works is https://whmcs-migration45265.blogdanica.com/26663321/top-cloudflare-free-ssl-secrets