From HEXONET Wiki
xDNS (extended DNS) - X-HTTP (Web-Forwarding)
X-HTTP records have the following syntax:
www.domain.com. 3600 IN X-HTTP REDIRECT http(s)://www.targetdomain.com
www.domain.com. 3600 IN X-HTTP FRAME http(s)://www.targetdomain.com
PLEASE NOTE: The secluding dot after the domain name (www.domain.com.) is required in any case!
www.mydomain.com. 3600 IN X-HTTP REDIRECT http://www.targetdomain.com
Result: Opening www.mydomain.com with a browser would redirect to http(s)://www.targetdomain.com with automatically changing www.mydomain.com to www.targetdomain.com in the browser address line. (“Header redirect”)
Using FRAME instead of REDIRECT would result in opening the target domain, but still showing www.mydomain.com in the browser address line (Target page embedded in a frame).
*.mydomain.com. 3600 IN X-HTTP REDIRECT http://www.targetdomain.com
Result: Opening any subdomain of mydomain.com (e.g. support.mydomain.com or admin.mydomain.com) would result in redirecting to http://www.targetdomain.com.
Instead of wildcarding (*.[...]) you can also provide an existing subdomain.