SMTP pool draft

gistfile1.cs

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Net.Mail;
using System.Threading;

namespace ConcurrentSMTP
{
    class Program
    {
        static void Main(string[] args)
        {
            // Example usage
            SMTPPool pool = new SMTPPool(() => new SmtpClient("yourhost.com"));
        }
    }

    class SMTPPool
    {
        private const byte MaxClients = 4;

        private int currentClients;
        private Func<SmtpClient> factory;
        private ConcurrentQueue<MailMessage> pendingMessages;

        public SMTPPool(Func<SmtpClient> factory)
        {
            this.factory = factory;
            this.pendingMessages = new ConcurrentQueue<MailMessage>();
            this.currentClients = 0;
        }

        private void CheckSpawns()
        {
            for (int i = MaxClients - 1; i >= 0; --i)
            {
                int value = Interlocked.CompareExchange(ref currentClients, i + 1, i);
                if(value == MaxClients){
                    return;
                } else if(value == i + 1){
                      SpawnProcess();
                      return;
                }
            }
        }

        public void AddMessage(MailMessage message)
        {
            pendingMessages.Enqueue(message);
            CheckSpawns();
        }

        public void AddMessages(List<MailMessage> messages)
        {
            messages.ForEach(AddMessage);
        }

        private async void SpawnProcess()
        {
            using (var client = factory()) {
                MailMessage message;
                while(pendingMessages.TryDequeue(out message)){
                    await client.SendMailAsync(message);
                }
            }
            Interlocked.Decrement(ref currentClients);
        }
        
    }
}