Sending an e-mail with an attachment through a .net application include these simple steps:-

1)- Use the following namespaces -
using System.Net;
using System.Net.Mail;
using System.IO;

2)- Call the following function where you have to send an email.

public void SendMail()
{
MailMessage msg = new MailMessage();
// Enter your mail id from which you have to send an email
msg.From = new MailAddress("sender email id");
// Enter your mail id to which you have to send an email
msg.To.Add("reciever email id");
msg.Body = "";
msg.IsBodyHtml = true;
msg.BodyEncoding = System.Text.Encoding.GetEncoding("utf-8");
Attachment at = new Attachment("Enter path of the file to attach");
msg.Attachments.Add(at);
msg.Subject = "Enter Message subject here ";
SmtpClient mailClient = new SmtpClient();
// Enter the smtp client here for example smtp client for gmail is smtp.gmail.com
mailClient.Host = "SMTP CLIENT";
msg.Body = "Enter Message Body here";
mailClient.Credentials = new System.Net.NetworkCredential("Sender Email ID", "Password");
mailClient.Send(msg);
mailClient.Dispose();
at.Dispose();
msg.Dispose();
}

Deleting the attachment after its sent away:-

3)- Call the following function to delete the attachment

protected void DeleteFile()
{
if (File.Exists("Enter path of the file")
{
File.Delete("Enter path of the file");
}
}

Please note that the attached file will not gets deleted unless all the resources used in sending mail have been released i.e calling of dispose method is mandatory as I have done in last 3 steps of the SendMail() function.