【C#】Smtp发送邮件

 class SmtpEmail
     {
         SmtpClient smtpclient;
         MailMessage msg;
         Attachment attachment;
         public void sendMail(String form, String[] to, String subject, String body, String attachmentpath)
         {
             if (to == null || to.Length <= ) {
                 return;
             }
             try
             {
                 smtpclient = new SmtpClient("smtp.URL");
                 smtpclient.UseDefaultCredentials = true;
                 smtpclient.Credentials = new NetworkCredential("username", "*****");
                 smtpclient.DeliveryMethod = SmtpDeliveryMethod.Network;
                 msg = new MailMessage();

                 for (int i = ; i < to.Length; i++)
                 {
                     msg.To.Add(to[i]);
                 }
                 if (msg.To.Count <= ) {
                     return;
                 }
                 msg.From = form;
                 msg.Subject = subject;
                 msg.Body = body;
                 if (attachment!=null && !attachmentpath.Length.Equals())
                 {
                     this.attachment = new Attachment(attachmentpath);
                     msg.Attachments.Add(attachment);
                 }
                 msg.BodyEncoding = Encoding.UTF8;
                 msg.IsBodyHtml = true;
                 smtpclient.Send(msg);
             }
             catch (Exception err)
             {
                 MessageBox.Show(err.Message);
                 return;
             }
         }
     }