必須using這兩個庫

using System.Net;

using System.Net.Mail;

某個按鈕下的語句

protected void BtnSendAEmail_Click(object sender, EventArgs e)
    {
        SmtpClient SendClient =new SmtpClient();                                   //新SmtpClient物件，使用163的SMTP伺服器
        SendClient.Host ="smtp.163.com";
        SendClient.Credentials = new NetworkCredential("例如

[email protected]", "認證密碼");    //必須到自己信箱中開啟smtp
        string FilePath;
        FilePath = Server.MapPath("");                                             //對映路徑，不使用固定編碼路徑
        Attachment MyAttchment = new Attachment(FilePath + "\\MailSendTest.txt");  //附件物件
       
        MailMessage WantSendMail=new MailMessage();                                //郵件物件
        WantSendMail.From = new MailAddress("iamt

[email protected]");
        WantSendMail.To.Add("[email protected]");
        WantSendMail.Subject = "標題";
        WantSendMail.Body = "主體";
        WantSendMail.Attachments.Add( MyAttchment );

        SendClient.Send(WantSendMail);
        WantSendMail.Attachments.Dispose();                                                    //必須釋放，否則無法編輯MailSendTest.txt
    }