WPForms Blacklist lets you blacklist / block submissions by keywords, blacklist / block email or complete email domains. It will help you avoiding a lot of spam from marketing companies.
WPForms Blacklist not only for blacklist it can be used as whitelist for example only allow invited email, guest name to submit form. It also support blacklist / white IP addresses or IPs in a specific country.
For more features you may check it from: WPForms Blacklist Features.
Instead showing error message in front, it also supports working as a QUIET SPAM BLOCKER. You may choose to skip notifications / go specific confirmation / delete entry if any keyword hit.
Easy to use:
Step 1, add the keywords / email address / IP address that you'd like to block / allow
Step 2, enable Blacklist form settings
Step 3, apply the blacklist / whitelist / email list / IP list to form field
For more details please check from: WPForms Blacklist.