Send Email with attachment in ASP.net

C# Code Behind

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;

public partial class _Default : System.Web.UI.Page 
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void btnSend_Click(object sender, EventArgs e)
    {
        MailMessage mail = new MailMessage();
        mail.To.Add(txtTo.Text);
        //mail.To.Add("amit_jain_online@yahoo.com");
        mail.From = new MailAddress(txtFrom.Text);
        mail.Subject = txtSubject.Text;
        mail.Body = txtMessage.Text;
        mail.IsBodyHtml = true;

        //Attach file using FileUpload Control and put the file in memory stream
        if (FileUpload1.HasFile)
        {
            mail.Attachments.Add(new Attachment(FileUpload1.PostedFile.InputStream, FileUpload1.FileName));
        }
        SmtpClient smtp = new SmtpClient();
        smtp.Host = "smtp.gmail.com"; //Or Your SMTP Server Address
        smtp.Credentials = new System.Net.NetworkCredential
             ("YourGmailID@gmail.com", "YourGmailPassword");
        //Or your Smtp Email ID and Password
        smtp.EnableSsl = true;
        smtp.Send(mail);

    }
}

VB.NET Code Behind

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

Public Partial Class _Default
    Inherits System.Web.UI.Page
    Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
        
    End Sub
    Protected Sub btnSend_Click(ByVal sender As Object, ByVal e As EventArgs)
        Dim mail As New MailMessage()
        mail.[To].Add(txtTo.Text)
        'mail.To.Add("amit_jain_online@yahoo.com");
        mail.From = New MailAddress(txtFrom.Text)
        mail.Subject = txtSubject.Text
        mail.Body = txtMessage.Text
        mail.IsBodyHtml = True
        
        'Attach file using FileUpload Control and put the file in memory stream
        If FileUpload1.HasFile Then
            mail.Attachments.Add(New Attachment(FileUpload1.PostedFile.InputStream, FileUpload1.FileName))
        End If
        Dim smtp As New SmtpClient()
        smtp.Host = "smtp.gmail.com"
        'Or Your SMTP Server Address
        smtp.Credentials = New System.Net.NetworkCredential("YourGmailID@gmail.com", "YourGmailPassword")
        'Or your Smtp Email ID and Password
        smtp.EnableSsl = True
            
        smtp.Send(mail)
    End Sub
End Class

Build and run the application to test the code.