Sending Emails from Desktop Application

<pre lang="xml">using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Linq;
using System.Net.Mail;
using System.Net.Mime;
using System.Text.RegularExpressions;
using System.Web;

namespace EmailHandler
{
    public class Emailer
    {
        /// <summary>
        /// Transmit an email message to a recipient without
        /// any attachments
        /// </summary>
        /// <param name="sendTo">Recipient Email Address</param>
        /// <param name="sendFrom">Sender Email Address</param>
        /// <param name="sendSubject">Subject Line Describing Message</param>
        /// <param name="sendMessage">The Email Message Body</param>
        /// <returns>Status Message as String</returns>
        public static string SendMessage(string sendTo, string sendFrom,
            string sendSubject, string sendMessage)
        {
            try
            {
                // validate the email address
                bool bTest = ValidateEmailAddress(sendTo);
                // if the email address is bad, return message
                if (bTest == false)
                    return "Invalid recipient email address: " + sendTo;
                // create the email message
                MailMessage message = new MailMessage(
                   sendFrom,
                   sendTo,
                   sendSubject,
                   sendMessage);
                // create smtp client at mail server location
                SmtpClient client = new SmtpClient(Properties.Settings.Default.SMTPAddress);
                // add credentials
                client.UseDefaultCredentials = true;
                // send message
                client.Send(message);
                return "Message sent to " + sendTo + " at " + DateTime.Now.ToString() + ".";
            }
            catch (Exception ex)
            {
                return ex.Message.ToString();
            }
        }

        /// <summary>
        /// Transmit an email message with
        /// attachments
        /// </summary>
        /// <param name="sendTo">Recipient Email Address</param>
        /// <param name="sendFrom">Sender Email Address</param>
        /// <param name="sendSubject">Subject Line Describing Message</param>
        /// <param name="sendMessage">The Email Message Body</param>
        /// <param name="attachments">A string array pointing to the location of each attachment</param>
        /// <returns>Status Message as String</returns>
        public static string SendMessageWithAttachment(string sendTo, string sendFrom,
            string sendSubject, string sendMessage, ArrayList attachments)
        {
            try
            {
                // validate email address
                bool bTest = ValidateEmailAddress(sendTo);
                if (bTest == false)
                    return "Invalid recipient email address: " + sendTo;
                // Create the basic message
                MailMessage message = new MailMessage(
                   sendFrom,
                   sendTo,
                   sendSubject,
                   sendMessage);
                // The attachments arraylist should point to a file location where
                // the attachment resides - add the attachments to the message
                foreach (string attach in attachments)
                {
                    Attachment attached = new Attachment(attach, MediaTypeNames.Application.Octet);
                    message.Attachments.Add(attached);
                }
                // create smtp client at mail server location
                SmtpClient client = new SmtpClient(Properties.Settings.Default.SMTPAddress);
                client.EnableSsl = true;
                // Add credentials
                client.UseDefaultCredentials = true;
                // send message
                client.Send(message);
                return "Message sent to " + sendTo + " at " + DateTime.Now.ToString() + ".";
            }
            catch (Exception ex)
            {
                return ex.Message.ToString();
            }
        }

        /// <summary>
        /// Confirm that an email address is valid
        /// in format
        /// </summary>
        /// <param name="emailAddress">Full email address to validate</param>
        /// <returns>True if email address is valid</returns>
        public static bool ValidateEmailAddress(string emailAddress)
        {
            try
            {
                string TextToValidate = emailAddress;
                Regex expression = new Regex(@"\w+@[a-zA-Z_]+?\.[a-zA-Z]{2,3}");
                // test email address with expression
                if (expression.IsMatch(TextToValidate))
                {
                    // is valid email address
                    return true;
                }
                else
                {
                    // is not valid email address
                    return false;
                }
            }
            catch (Exception)
            {
                throw;
            }
        }
    }
}

<pre lang="xml">using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using EmailHandler;

namespace EmailTestApp
{
    /// <summary>
    /// Test Application Form:
    /// This application is used to test sending
    /// email and email with attachments.
    /// </summary>
    public partial class frmTestEmail : Form
    {
        /// <summary>
        /// An arraylist containing
        /// all of the attachments
        /// </summary>
        ArrayList alAttachments;

        /// <summary>
        /// Default constructor
        /// </summary>
        public frmTestEmail()
        {
            InitializeComponent();
        }

        /// <summary>
        /// Add files to be attached to the email message
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnAdd_Click(object sender, EventArgs e)
        {
            if (openFileDialog1.ShowDialog() == DialogResult.OK)
            {
                try
                {
                    string[] arr = openFileDialog1.FileNames;
                    alAttachments = new ArrayList();
                    txtAttachments.Text = string.Empty;
                    alAttachments.AddRange(arr);
                    foreach (string s in alAttachments)
                    {
                        txtAttachments.Text += s + "; ";
                    }
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.Message, "Error");
                }
            }
        }

        /// <summary>
        /// Exit the application
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnCancel_Click(object sender, EventArgs e)
        {
            Application.Exit();
        }

        /// <summary>
        /// Send an email message with or without attachments
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnSend_Click(object sender, EventArgs e)
        {
            if (String.IsNullOrEmpty(txtSendTo.Text))
            {
                MessageBox.Show("Missing recipient address.", "Email Error");
                return;
            }
            if (String.IsNullOrEmpty(txtSendFrom.Text))
            {
                MessageBox.Show("Missing sender address.", "Email Error");
                return;
            }
            if (String.IsNullOrEmpty(txtSubjectLine.Text))
            {
                MessageBox.Show("Missing subject line.", "Email Error");
                return;
            }
            if (String.IsNullOrEmpty(txtMessage.Text))
            {
                MessageBox.Show("Missing message.", "Email Error");
                return;
            }
            string[] arr = txtAttachments.Text.Split(';');
            alAttachments = new ArrayList();
            for (int i = 0; i < arr.Length; i++)
            {
                if (!String.IsNullOrEmpty(arr[i].ToString().Trim()))
                {
                    alAttachments.Add(arr[i].ToString().Trim());
                }
            }
            // if there are attachments, send message with
            // SendMessageWithAttachment call, else use the
            // standard SendMessage call
            if (alAttachments.Count > 0)
            {
                string result = Emailer.SendMessageWithAttachment(txtSendTo.Text,
                    txtSendFrom.Text, txtSubjectLine.Text, txtMessage.Text,
                    alAttachments);
                MessageBox.Show(result, "Email Transmittal");
            }
            else
            {
                string result = Emailer.SendMessage(txtSendTo.Text,
                    txtSendFrom.Text, txtSubjectLine.Text, txtMessage.Text);
                MessageBox.Show(result, "Email Transmittal");
            }
        }

    }
}