title: Longer domain name extension and ASP.NET MVC validation
body: <p>A customer complained about not being able to register to our ASP.NET MVC website because his email is like the following:</p>
  
  <pre><code>name.surname@innovation.world 
  </code></pre>
  
  <p>Here is the standard ASP.NET MVC <code>RegisterModel</code>:</p>
  
  <pre><code>public class RegisterModel
  {
      [Required]
      [Display(Name = "User name")]
      public string UserName { get; set; }
  
      [Required]
      [DataType(DataType.EmailAddress)]
      [Display(Name = "Email")]
      [RegularExpression(@"^[_a-zA-Z0-9-]+(\.[_a-zA-Z0-9-]+)*@[a-zA-Z0-9-]+(\.[a-zA-Z0-9-]+)*(\.[a-zA-Z]{2,4})$", ErrorMessage = "Email must be valid")]
      public string Email { get; set; }
  
      ...
  }
  </code></pre>
  
  <p>How do I change the regular expression to take in account these new longer domain name extensions?</p>
  
  <p>Thanks.</p>