title: Ruby Regex to extract domain from email address
body: <p>I have no real previous experience using regex, just saying.
  I want to extract domain names from email addresses with the below format.</p>
  
  <p>richardc@mydomain.com
  so that the regex returns just: mydomain</p>
  
  <p>With an explanation of how/why it works if possible!
  Cheers</p>