ExtractEmails*-regex

using System;
using System.Text.RegularExpressions;
namespace text
{
    class MainClass
    {
        public static void Main(string[] args)
        {
            string input = Console.ReadLine();
            Regex regexForEmail=new Regex(@"(?<=\s)(?<user>(?![_])[A-za-z0-9]+(?:[\.\-_][A-za-z0-9]+)*)@(?<host>[a-zA-Z]+(?:[\-][a-zA-z]+)*(?:\.[a-zA-Z]+(?:[\-][a-zA-Z]+)*)*\.[a-z]+)");// NB! VS is not running regex with "\_"
            MatchCollection matchesEmail = regexForEmail.Matches(input);
            if (regexForEmail.IsMatch(input))
            {
                foreach (Match match in matchesEmail)
                {
                    Console.Write(match.Groups["user"]);
                    Console.Write("@");
                    Console.WriteLine(match.Groups["host"]);
                }
            }

        }
    }
}