Opens the files specified and strips out the emails

program.cs

namespace ExtractEmails
{
    using System;
    using System.Collections.Concurrent;
    using System.IO;
    using System.Linq;
    using System.Text.RegularExpressions;

    public class Program
    {
        private static ConcurrentDictionary<string, int> emails = new ConcurrentDictionary<string, int>();

        public static void Main(string[] args)
        {          
            args.AsParallel()
                .Select(x => new FileInfo(x))
                .Where(x => x.Exists)
                .ForAll(x =>
                {
                    var regex = new Regex("[a-z0-9!#$%&\'*+/=?^_`{|}~-]+(?:\\.[a-z0-9!#$%&\'*+/=?^_`{|}~-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?");
                    using (var text = x.OpenText())
                        while (text.EndOfStream == false)
                        {
                            var readLine = text.ReadLine();
                            var match = regex.Match(readLine);
                            AddIfMatched(match);
                        }
                });

            using (var writer = File.CreateText("results.txt"))
                foreach (var e in emails)
                {
                    writer.WriteLine(e.Key + ", " + e.Value);
                }
        }

        private static void AddIfMatched(Match match)
        {
            if (match.Success == false) return;

           var email = match.Captures[0];
           emails.AddOrUpdate(email.Value, 1, (s, i) => ++i);

           AddIfMatched(match.NextMatch());
        }
    }
}