Uset.cs

using System;
using System.Text.RegularExpressions;
class User 
    {

        int _id;
        string _login;
        string _password;
        string _email;

        public string Email
        {
            set
            {
                string pat = @" ^(?("")("".+?""@)|
                              (([0-9a-zA-Z]((\.(?!\.))
                              |[-!#\$%&'\*\+/=\?\^`\{\}\|
                               ~\w])*)(?<=[0-9a-zA-Z])@))
                              (?(\[)(\[(\d{1,3}\.){3}\d{1,3}\])|
                              (([0-9a-zA-Z][-\w]*[0-9a-zA-Z]\.)
                              +[a-zA-Z]{2,6}))$"; // regexp mak
                if (!(new Regex(pat)).IsMatch(value))
                    throw new ArgumentOutOfRangeException("Email"); 
                _email = value;
            }
            get 
            {
                return _email;
            }
        }
        
    }