Email Address validation for ASP.NET MVC

EmailAddressAttribute.cs

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Text.RegularExpressions;
using System.Web.Mvc;

namespace MyApp.Web.PresentationLogic.Validation
{
  [AttributeUsage(AttributeTargets.Property, AllowMultiple = false)]
	public sealed class EmailAddressAttribute : DataTypeAttribute, IClientValidatable
	{
		private static Regex _regex = new Regex(@"^((([a-z]|\d|[!#\$%&'\*\+\-\/=\?\^_`{\|}~]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])+(\.([a-z]|\d|[!#\$%&'\*\+\-\/=\?\^_`{\|}~]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])+)*)|((\x22)((((\x20|\x09)*(\x0d\x0a))?(\x20|\x09)+)?(([\x01-\x08\x0b\x0c\x0e-\x1f\x7f]|\x21|[\x23-\x5b]|[\x5d-\x7e]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(\\([\x01-\x09\x0b\x0c\x0d-\x7f]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF]))))*(((\x20|\x09)*(\x0d\x0a))?(\x20|\x09)+)?(\x22)))@((([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])([a-z]|\d|-|\.|_|~|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])*([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])))\.)+(([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])([a-z]|\d|-|\.|_|~|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])*([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])))\.?$", RegexOptions.Compiled | RegexOptions.IgnoreCase);

		public EmailAddressAttribute()
			: base(DataType.EmailAddress)
		{
			ErrorMessage = "The {0} field is not a valid e-mail address.";
		}

		public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context)
		{
			yield return new ModelClientValidationRule
			{
				ValidationType = "email",
				ErrorMessage = FormatErrorMessage(metadata.GetDisplayName())
			};
		}

		public override bool IsValid(object value)
		{
			if (value == null)
			{
				return true;
			}

			string valueAsString = value as string;

			return valueAsString != null && _regex.Match(valueAsString).Length > 0;
		}
	}
}