"You cannot send more than 5 messages in 1 hour" I have several contact forms, but I don't want to limit the users to submit the form. I've tried form unblock with smart IP; it doesn't work for me.

Do you have any idea to release the IP and unset the limit?
Change it using drush config-set. 

To get the default settings use:

drush config-get contact.settings


To change the limit to 100 instead of 5, use:

drush config-set contact.settings flood.limit 100