Note: In addition to the flow described below, it is also possible (and often easier) to set up a free account on Cloudflare which offers this feature as part of their free solution and provides a dedicated SSL certificate for a small fee.
What are domains?
Domains are simply human-friendly aliases for IP addresses (side-note: a domain can be an alias to a “pool” of IP addresses, to spread requests over multiple servers). For example, “google.com” is an alias for the IP addresses 220.127.116.11, 18.104.22.168, 22.214.171.124 etc. These are all servers that Google Inc. own, and can respond to requests to search the Internet.
In the setup instructions for HTTP “Custom Domains” in the Dynamic Yield Admin panel, it is said that in order for a Custom Domain to work it must be defined as a “CNAME” of “srv.dynamicyield.com”. This means that your custom domain (for example, “lp.customer.com”) is an alias for “srv.dynamicyield.com” which in itself is an alias of the pool of Dynamic Yield servers. That way, when a visitor clicks on a link to “http://lp.customer.com/new-deal” his request is directed to the Dynamic Yield servers that know how to find the Landing Page “/new-deal” of “Customer.com” and how to serve it back to the visitor.