static void Main(string[] args)
{
string str = File.ReadAllText("1.txt", Encoding.Default);
MatchCollection mc = Regex.Matches(str, @"([-a-zA-Z_0-9.]+)@([-a-zA-Z0-9_]+(\.[a-zA-Z]+)+)");
foreach (Match m in mc)
{
Console.WriteLine(m.Value);
Console.WriteLine(m.Groups[2].Value);//([-a-zA-Z_0-9.]+)@([-a-zA-Z0-9_]+(\.[a-zA-Z]+)+)")这是第一组，([-a-zA-Z_0-9.]+)第二组([-a-zA-Z0-9_]+(\.[a-zA-Z]+)+)")第三组(\.[a-zA-Z]+)+)第四组
Console.WriteLine("=========");
}
Console.WriteLine(mc.Count);
Console.ReadKey();
}