In ASP.NET MVC 4, using the Entity Framework (code first) approach, I needed to create a RegEx for emails - allowing uppercase or lowercase. This was the solution for me.

Email(property).cs

 [Required]
 [RegularExpression(@"\b[A-Z0-9._%+-]+@(?:[A-Z0-9-]+\.)+[A-Z]{2,4}\b", ErrorMessage = "Invalid email address")]
 [DisplayName("E-mail addresss")]  
 public string Email { get; set; }