How to send Email using asp.net

First we need to import System.Web.Mail namespace. The system.Web.Mail namespace contains classes that enable you to construct and send messages using the CDOSYS message component.

To Add this reference follow below steps

1)On the project menu click add reference

2)After That click .net Tab, locate System.Web.ddl, and then click Select.
3)Click ok in the add references.


Design Page

<?xml version="1.0"?>
<!-- 
    Note: As an alternative to hand editing this file you can use the 
    web admin tool to configure settings for your application. Use
    the Website->Asp.Net Configuration option in Visual Studio.
    A full list of settings and comments can be found in 
    machine.config.comments usually located in 
    \Windows\Microsoft.Net\Framework\v2.x\Config 
-->
<configuration>
	<appSettings/>
	<connectionStrings/>
	<system.web>
		<!-- 
            Set compilation debug="true" to insert debugging 
            symbols into the compiled page. Because this 
            affects performance, set this value to true only 
            during development.
        -->
		<compilation debug="true"/>
		<!--
            The <authentication> section enables configuration 
            of the security authentication mode used by 
            ASP.NET to identify an incoming user. 
        -->
		<authentication mode="Windows"/>
		<!--
            The <customErrors> section enables configuration 
            of what to do if/when an unhandled error occurs 
            during the execution of a request. Specifically, 
            it enables developers to configure html error pages 
            to be displayed in place of a error stack trace.

        <customErrors mode="RemoteOnly" defaultRedirect="GenericErrorPage.htm">
            <error statusCode="403" redirect="NoAccess.htm" />
            <error statusCode="404" redirect="FileNotFound.htm" />
        </customErrors>
        -->
	</system.web>
</configuration>

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Net.Mail;
using System.Net;

public partial class _Default : System.Web.UI.Page 
{    
    protected void btnSend_Click(object sender, EventArgs e)
    {
        try
        {
            MailMessage msg = new MailMessage(txtFromMailID.Text.ToString().Trim(), txtTomailid.Text.ToString().Trim(), txtsubject.Text.ToString(), txtbody.Text.ToString());
            MailAddress SendCC = new MailAddress(txtCC.Text.ToString());
            msg.CC.Add(SendCC);
            SmtpClient mailClient = new SmtpClient(txtsmtpaddress.Text.ToString().Trim(), Convert.ToInt32(txtPortAddress.Text.ToString().Trim()));
            NetworkCredential NetCrd = new NetworkCredential(txtFromMailID.Text.ToString(), txtPassword.Text.ToString());
            mailClient.UseDefaultCredentials = false;
            mailClient.Credentials = NetCrd;
            if (Convert.ToInt32(txtPortAddress.Text.ToString().Trim()) == 587)
            {
                mailClient.EnableSsl = true;
            }
            else
            {
                mailClient.EnableSsl = false;
            }
            mailClient.DeliveryMethod = SmtpDeliveryMethod.Network;

            mailClient.Send(msg);
            Page.ClientScript.RegisterStartupScript(this.GetType(), "alertScript", "Mail Sent", true);
         }
        catch (Exception ex)
        {            Page.ClientScript.RegisterStartupScript(this.GetType(), "alertScript", ex.Message, true);
        }
    }
}