Settings:
Domain: require the "fully qualified domain name" (fqdn), like "mydomain.com" or "www.mydomain.com".
Username: your easydns username.
Password: your easydns 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 dynu support pages.