And I would like user registration to be combined with subscription to my mailing list.
So for instance if a user isn't logged in, they are limited to 5 uses per day (based on IP/cookie etc.). And if they are logged in, they can use the tool 25 times per day
Note that registration will be free (I'm not looking to sell anything).
What plugins or tools are out there that can do this - combine mailing list subscription with user registration, and content restriction? Are there mailing list providers who offer an official content restriction solution?