title: Rails, validates email exclusion
body: <p>I'm currently trying to validates an email attributes with few things :</p>
  
  <ol>
  <li>Its presence</li>
  <li>Its format with a regex</li>
  <li>Its uniqueness</li>
  <li>Its non presence in a list of mail providers</li>
  </ol>
  
  <p>I'm stuck at the fourth step, I don't really know how to implement it, the main of this steps is to exclude throwable mail providers.</p>
  
  <p>I've currently this :</p>
  
  <pre><code>  validates :email, :presence   =&gt; true,
                      :format     =&gt; { :with =&gt; email_regex },
                      :uniqueness =&gt; { :case_sensitive =&gt; false },
                      :exclude =&gt; Not working when I put a regex here
  </code></pre>
  
  <p>My problem isn't the regex, it's how to exclude email matching with exclude regex.</p>
  
  <p>Can you help me do this ?</p>
  
  <p>Cordially, Rob.</p>