you can you below code from your problem
if (FileUpload1.HasFile)
{
string toAddress = "you@yourprovider.com";
string fromAddress = "you@yourprovider.com";
string mailServer = "smtp.yourprovider.com";
MailMessage myMailMessage = new MailMessage();
myMailMessage.To.Add(toAddress);
myMailMessage.From = new MailAddress(fromAddress);
myMailMessage.Subject = "Test Message";
string fileName = Path.GetFileName(FileUpload1.PostedFile.FileName);
Attachment myAttachment =
new Attachment(FileUpload1.FileContent, fileName);
myMailMessage.Attachments.Add(myAttachment);
SmtpClient mySmtpClient = new SmtpClient(mailServer);
mySmtpClient.Send(myMailMessage);
}