Dyndns.org was the first service supported by DirectUpdate.
The page about client updater is amazing ! Check
it out and vote for DirectUpdate :)
Settings:
Domain: require the "fully qualified domain name" (fqdn), like "mydomain.dyndns.org" or "mydomain.homeip.net".
Username: your dyndns username.
Password: your dyndns password.
Advanced settings:
Enable wildcard: check this box to be able to use *.mydomain.dyndns.org and not only mydomain.dyndns.org
MX domain: enter here the server address for your MaileXchanger (leave blank if unknown).
Backup MX: Check this box if the above address is your secondary MX (it means mydomain.dyndns.org will be your primary MX).
For more info, visit the dyndns support pages.