using System;
using System.Globalization;
using System.Text.RegularExpressions;

public class RegexUtilities
{
    public static bool IsValidEmail(string email)
    {
        if (string.IsNullOrWhiteSpace(email))
            return false;
        try
        {
            // Normalize the domain
            email = Regex.Replace(email, @"(@)(.+)$", DomainMapper,
                                  RegexOptions.None, TimeSpan.FromMilliseconds(200));

            // Examines the domain part of the email and normalizes it.
            string DomainMapper(Match match)
            {
                // Use IdnMapping class to convert Unicode domain names.
                var idn = new IdnMapping();

                // Pull out and process domain name (throws ArgumentException on invalid)
                var domainName = idn.GetAscii(match.Groups[2].Value);

                return match.Groups[1].Value + domainName;
            }
        }
        catch (RegexMatchTimeoutException e)
        {
            return false;
        }
        catch (ArgumentException e)
        {
            return false;
        }

        try
        {
            return Regex.IsMatch(email,
                @"^(?("")("".+?(?<!\\)""@)|(([0-9a-z]((\.(?!\.))|[-!#\$%&'\*\+/=\?\^`\{\}\|~\w])*)(?<=[0-9a-z])@))" +
                @"(?(\[)(\[(\d{1,3}\.){3}\d{1,3}\])|(([0-9a-z][-0-9a-z]*[0-9a-z]*\.)+[a-z0-9][\-a-z0-9]{0,22}[a-z0-9]))$",
                RegexOptions.IgnoreCase, TimeSpan.FromMilliseconds(250));
        }
        catch (RegexMatchTimeoutException)
        {
            return false;
        }
    }
}