title: Blacklist Domains from Email Field + Correct Format
body: <p>I have a client that would like to blacklist 300+ competitor domains from being entered into their email fields on their HTML forms. They would like to also only accept emails in the format hello@domain.extension.</p>
  
  <p>If an incorrect email is entered a rejection message should either appear immediately or after one presses submit.</p>
  
  <p>How would I go about achieving this?</p>