Create MailHelper.cs into an App_Code
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using System.Net.Mail;

public class MailHelper
{
    /// <summary>
    /// Sends an mail message
    /// </summary>
    /// <param name="from">Sender address</param>
    /// <param name="to">Recepient address</param>
    /// <param name="bcc">Bcc recepient</param>
    /// <param name="cc">Cc recepient</param>
    /// <param name="subject">Subject of mail message</param>
    /// <param name="body">Body of mail message</param>
    public static void SendMailMessage(string from, string to, string bcc, string cc, string subject, string body)
    {
        // Instantiate a new instance of MailMessage
        MailMessage mMailMessage = new MailMessage();

        // Set the sender address of the mail message
        mMailMessage.From = new MailAddress(from);
        // Set the recepient address of the mail message
        mMailMessage.To.Add(new MailAddress(to));

        // Check if the bcc value is null or an empty string
        if ((bcc != null) && (bcc != string.Empty))
        {
            // Set the Bcc address of the mail message
            mMailMessage.Bcc.Add(new MailAddress(bcc));
        }      // Check if the cc value is null or an empty value
        if ((cc != null) && (cc != string.Empty))
        {
            // Set the CC address of the mail message
            mMailMessage.CC.Add(new MailAddress(cc));
        }       // Set the subject of the mail message
        mMailMessage.Subject = subject;
        // Set the body of the mail message
        mMailMessage.Body = body;

        // Set the format of the mail message body as HTML
        mMailMessage.IsBodyHtml = true;
        // Set the priority of the mail message to normal
        mMailMessage.Priority = MailPriority.Normal;

        // Instantiate a new instance of SmtpClient
        SmtpClient mSmtpClient = new SmtpClient();
        mSmtpClient.EnableSsl = true;
        // Send the mail message
        mSmtpClient.Send(mMailMessage);
    }
}
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Web.Config
add the following line


<system.net>
		<mailSettings>
			<smtp from="youremail@gmail.com">
				<network host="smtp.gmail.com" port="587" userName="youremail" password="yoourpassword"/>
			</smtp>
		</mailSettings>
	</system.net>
-----------------------------------
Send email code

string body="At " + DateTime.Now + " feedback was sent from an ASP.NET " +
                   "Web page.  Below you will find the feedback message " +
                   "send by " + txtName.Text + "." +
                   "---------------------------------------" +txtMessage.Text;
        MailHelper.SendMailMessage("yourmail@gmail.com", txtEmail.Text, "", "", "Testing", body);
        panelSendEmail.Visible = false;
        panelMailSent.Visible = true;