That almost made me quit right there, but I decided to check out the fine print, as per the links in the dialog.
And when I want to the web site to post a question about this, they wanted me to register first.
So much for doubleTwist. I’m not giving someone my e-mail without knowing more.
Addendum: Apparently Help > Contact Support uses regular e-mail, so there is at least a standard way to contact them.