DDDNS (Delegated Dynamic DNS) ensures that if your
dynamic DNS name resolves, then it is because your
server is present (i.e. connected to the network).
This is done by delegating a DNS sub-zone to your
current IP address. If your server is not present,
or if another server has taken your former IP
address, the name does not resolve. DDDNS uses
nsupdate to send RFC2136 updates to the upstream
DNS server. DDDNS names are fail-safe for mail
delivery and general hosting.
