// Expresión regular que coincida también con mayúsculas
// http://es.stackoverflow.com/a/50127/127
 
using System;
using System.Text.RegularExpressions;
 
public class Test
{
    public static bool ValidarEmail(String email)
    {
        String expresion = @"^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,4})$";
 
        return Regex.IsMatch(email, expresion, RegexOptions.IgnoreCase);
    }
 
 
    public static void Main()
    {
        //Pruebas
        string[] pruebas = {"tucorreo-@hotmail.com",
                            "tucorreo_@hotmail.com",
                            "Tucorreo_._@hotmail.com",
                            "este.es@un.mail.incorrecto"};
        foreach (string email in pruebas)
        {
            if (ValidarEmail(email))
            {
                Console.WriteLine("'{0}' es válido", email);
            }
            else
            {
                Console.WriteLine("'{0}' no es un email válido", email);
            }
        }
    }
}

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