I am using the Domain Mapping plugin from WPMUDEV.org and I understand that I'm supposed to get with them for support but my subscriptions has expired. I just upgraded to WP 3.0 multisite and I trying to get my mapped domain to work with 'www'. My domain is registered with godaddy.com and I have gone in there and configured CNAME record to have http://www.mydomain.com mapped to blog.mywpblog.com. The plugin on my WP multisite is configured correctly on blog.mywpblog.com but every time I type the url http://www.mydomain.com, I'm sent to the sign up page for my website to create a new account.
One more thing, if I use the A record setting without the 'www', the mapped domain works. Please, help me anyone. Thanks.