From HEXONET Wiki
xDNS (extended DNS) - Web-Forwarding, Email-Forwarding and DNS Alias handling
xDNS is a proprietary extension to standard DNS that allows to setup Web-Forwarding, Email-Forwarding and Alias resource records as easy as any other DNS resource records for a DNS zone.
You can provide xDNS records with the CreateDNSZone API command and the UpdateDNSZone API command but you need to submit the additional parameter "EXTENDED = 1".
Possible extended DNS records are: