Send mail tool

using System;
using System.Net.Mail;
using System.Net;

namespace Bruce.Mail
{
    public class MailFactory
    {
        private static SmtpClient client;
        public static void SetSmtp(string smtpHost, int smtpPort, string username, string password)
        {
            SetSmtp(smtpHost, smtpPort);
            client.UseDefaultCredentials = false;
            client.Credentials = new NetworkCredential(username, password);
        }
        public static void SetSmtp(string smtpHost, int smtpPort)
        {
            client = new SmtpClient(smtpHost, smtpPort);
        }
        public static void SetSmtp()
        {
            client = new SmtpClient();
        }

        private MailMessage message;
        public MailMessage Message
        {
            get { return this.message; }
        }

        public MailFactory()
        {
            this.message = new MailMessage();
        }

        public MailFactory(MailAddress from, MailAddress to)
        {
            this.message = new MailMessage(from, to);
        }

        public MailFactory(string fromName, string fromAddress, string toName, string toAddress)
        {
            MailAddress from = string.IsNullOrEmpty(fromName) ? new MailAddress(fromAddress) : new MailAddress(fromAddress, fromName);
            MailAddress to = string.IsNullOrEmpty(toName) ? new MailAddress(toAddress) : new MailAddress(toAddress, toName);
            this.message = new MailMessage(from, to);
        }

        public void Write(string subject, string body)
        {
            this.message.Subject = subject;
            this.message.IsBodyHtml = false;
            this.message.Body = body;
            this.Send();
        }

        public Exception Send()
        {
            try
            {
                if (client == null) SetSmtp();
                client.Send(this.message);
                return null;
            }
            catch (Exception ex)
            {
                return ex;
            }
        }
    }
}

using System;
using System.Net.Mail;
using System.Collections.Generic;
using System.Threading;

namespace Bruce.Mail
{
    public abstract class PostMan
    {
        private static Queue<MailAddress> Recivers = new Queue<MailAddress>();
        public static void AddReciver(MailAddress address)
        {
            Recivers.Enqueue(address);
        }
        public static void AddReciver(string address)
        {
            Recivers.Enqueue(new MailAddress(address));
        }

        private int checkInterval;
        public int CheckInterval
        {
            get { return this.checkInterval; }
            set { this.checkInterval = value; }
        }
        private bool flag = true;
        public bool Flag
        {
            get { return this.flag; }
            set { this.flag = value; }
        }

        public void Work()
        {
            while (Flag)
            {
                if (Recivers.Count == 0)
                {
                    Thread.Sleep(30000);
                }
                else
                {
                    MailAddress to = Recivers.Dequeue();
                    Deliver(to);
                }
            }
        }

        abstract void Deliver(MailAddress to);
    }
}