using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        var textToTest = "RobC@QuickLearn.com, NickH@Hotmail.com";

        var regEx = "(@[A-z0-9.]*)";

        var result = Regex.Match(textToTest, regEx);

        Console.WriteLine(result.Value);

    }

}