How To Send Email With ASP.NET C#

using System;
using System.Net.Mail;
//using System.Web.Mail;

/// <summary>
/// Summary description for commonClass
/// </summary>
public class mailClass
{
    #region Declaration
    string retMsg = "";
    private string m_toEmail;
    private string m_fromEmail;
    private string m_displayName;
    private string m_subject;
    private string m_body;
    private string m_bcc;
    private Attachment m_attachment;
    const string c_success = "success";
    const string c_error = "error";
    #endregion 

    public mailClass()
    {
        //
        // TODO: Add constructor logic here
        //
    }

    #region Properties
    public string vToEmail
    {
        get
        {
            return m_toEmail;
        }
        set
        {
            if (value != m_toEmail)
            {
                m_toEmail = value;
            }
        }
    }

    public string vFromEmail
    {
        get
        {
            return m_fromEmail;
        }
        set
        {
            if (value != m_fromEmail)
            {
                m_fromEmail = value;
            }
        }
    }
    public string vDisplayName
    {
        get
        {
            return m_displayName;
        }
        set
        {
            if (value != m_displayName)
            {
                m_displayName = value;
            }
        }
    }
    public string vSubject
    {
        get
        {
            return m_subject;
        }
        set
        {
            if (value != m_subject)
            {
                m_subject = value;
            }
        }
    }
    public string vBody
    {
        get
        {
            return m_body;
        }
        set
        {
            if (value != m_body)
            {
                m_body = value;
            }
        }
    }
    public Attachment vAttachment
    {
        get
        {
            return m_attachment;
        }
        set
        {
            if (value != m_attachment)
            {
                m_attachment = value;
            }
        }
    }



    public string vBcc
    {
        get
        {
            return m_bcc;
        }
        set
        {
            if (value != m_bcc)
            {
                m_bcc = value;
            }
        }
    }
    #endregion

    #region Function
    public string SendMail()
    {
        try
        {
            MailAddress from = new MailAddress(m_fromEmail, "World Class Medals");
            MailMessage message = new MailMessage();
            SmtpClient emailClient = new SmtpClient("smtp.appliedi.net");
            System.Net.NetworkCredential SMTPUserInfo = new System.Net.NetworkCredential("", "");
            emailClient.UseDefaultCredentials = false;
            emailClient.Credentials = SMTPUserInfo;
            if (m_toEmail.Contains(";"))
            {
                message = new MailMessage();
                string[] addrCollection = m_toEmail.Split(";".ToCharArray());
                string mailList = "";
                foreach (string addr in addrCollection)
                    mailList = mailList + "<" + addr + "> ,";
                mailList = mailList.TrimEnd(",".ToCharArray());
                MailAddress to = new MailAddress(mailList);
                message = new MailMessage(from, to);
            }
            else
            {
                MailAddress to = new MailAddress(m_toEmail);
                message = new MailMessage(from, to);
            }
            if (m_bcc != null)
            {
                MailAddress bcc = new MailAddress(m_bcc);
                message.Bcc.Add(bcc);
            }
            message.IsBodyHtml = true;
            message.Subject = m_subject;
            message.Body = m_body;
            if (this.vAttachment != null)
                message.Attachments.Add(this.vAttachment);
            emailClient.Send(message);
            retMsg = c_success;
        }
        catch (Exception ex)
        {
            retMsg = ex.Message.ToString();
        }
        return retMsg;
    }
    #endregion 

}

<appSettings> In the webconfig file add this
            <add key="to" value="cparole@imtsus.com"/>
    <add key ="to" value="druiz@imtsus.com"/>
    <add key ="to" value="rmiller@imtsus.com"/>
    <add key ="to" value="rdasan@imtsus.com"/>
            <add key="from" value="avilparackal@gmail.com"/>
            <add key="id" value="Ur gmail"/>
            <add key="pswd" value="Password""/>
            <add key="port" value="587"/>
            <add key="smtp" value="smtp.gmail.com"/>
      </appSettings>

private void sendmail()
  {

      try
      {
    str_mailer.Append(@"<b>Name : </b>  " + txtsubject.Text);
             str_mailer.Append(@"\n\n\n\ <b>Email Address : </b>" + txtmessage.Text );
             str_mailer.Append(@"<br/><b>Phone No : </b>" + txtTo.Text);
             //str_mailer.Append(@"<br/><b>Type Of Service : </b>" + dd_select.Text );
             //str_mailer.Append(@"<br/><b>Estimated Budget : </b>" + dd_budget.Text);
             //str_mailer.Append(@"<br/>" + "<b>Comment : </b>" + txt_comment.Text );
             //str_mailer.Append(@"<br/>" + "<b>How Did You hear about Us : </b>" + txtget_id.Text);
             //below line m giving  sender's email address  and receiever's email address  that is also mentioned inside the <appSettings></appSettings> in the web.config file
             // and m also giving str_mailer.ToString() , in the str_mailer.ToString() coming  completed message with the html tags
             System.Net.Mail.MailMessage mail = new System.Net.Mail.MailMessage(ConfigurationManager.AppSettings["id"], ConfigurationManager.AppSettings["to"], "Info", str_mailer.ToString());
             //below line m giving  sender's email address and password of that email that is mentioned inside the <appSettings></appSettings> in the web.config file
             System.Net.NetworkCredential mailAuthentication = new System.Net.NetworkCredential(ConfigurationManager.AppSettings["id"], ConfigurationManager.AppSettings["pswd"]);
             //below line m giving  smtp and port no: that is also mentioned inside the <appSettings></appSettings> in the web.config file
            System.Net.Mail.SmtpClient mailClient = new System.Net.Mail.SmtpClient(ConfigurationManager.AppSettings["smtp"], Convert.ToInt32(ConfigurationManager.AppSettings["port"]));
            //System.Net.Mail.SmtpClient mailClient = new System.Net.Mail.SmtpClient("smtp.gmail.com", 587);
            //below m setting some important properties that is necessary to send the email
            mailClient.EnableSsl = true;
            //below property IsBodyHtml in true because inside the stringbuilder am using some HTMl tags
            mail.IsBodyHtml = true;
            mailClient.UseDefaultCredentials = false;
            mailClient.Credentials = mailAuthentication;
            mailClient.Send(mail);
            // when all the process will be completed then a message will be displayed inside the label
            lbl_msg.Text = "Thank you, your mail has been sent successfully.";
        }


        catch
        {



                lbl_msg.Text = "Please wait..";
                sendmail();


        }

    }



    protected void btnsend_Click(object sender, EventArgs e)
    {
 sendmail();
    }