How to limit submissions based on a unique question.

1) If a user has already given me his email and his name, how can i "block" his second subscription? I've tried to subscribe the same email for two times and the subscription has been duplicated. 

If you want to limit a submission based on a unique answer, then follow this guide: https://www.jotform.com/help/223-How-to-set-Form-Limits-Based-on-a-Unique-Question 

Your second question will be addressed in the following thread: https://www.jotform.com/answers/1353489