using System;

using System.Collections.Generic;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        string input = "Reuben.olsen@kotahi.co.nz";

        bool output = validateEmail(input);

        Console.WriteLine(output);

    }

 private static bool validateEmail(string _email)

    {

        /* This regex validates the following structure for an email address:

        a. Contains a '@' character

        b. Contains a period after '@'

        c. Has only one @ and at least one character before the @, before the period and after it

        */

        string emailAddressFilter = "^(?(\")(\".+?(?<!\\\\)\"@)|(([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]))$";

​

        System.Text.RegularExpressions.Regex regEx;

        System.Text.RegularExpressions.Match regMatch;

        string email;

        List<string> emailAddresses;

        bool retVal= false;

        //BP Deviation documented

        regEx = new System.Text.RegularExpressions.Regex(emailAddressFilter, System.Text.RegularExpressions.RegexOptions.IgnoreCase);

​

        // Split the email address string and validate each email address

        emailAddresses = new List<string>(_email.Split(';'));

        var enume = emailAddresses.GetEnumerator();

        while(enume.MoveNext())

        {

            email = enume.Current;

​

            if (!string.IsNullOrEmpty(email))

            {

                regMatch = regEx.Match(email);

                retVal = regMatch.Success;

            }

            else

                retVal = false;

​

            // If a single email address is invalid, the string is invalid

            if(!retVal)

                break;

        }

​

        return retVal;

    }

}