I have a question with contact emails flood limit which is present in contact.settings.yml, the limit is going to for whole system(application-wide) or is it going to limit the number of emails per individual user or IP?
As you can see its number of emails a user can send in an hour
You can specify the text to display on your site-wide contact page and you can optionally limit how many times a user can submit a contact form in an hour.
btw, its defaults that you can override per any contact form . for example :
default_form: feedback flood: limit: 5 interval: 3600 user_default_enabled: true