【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 <= 0) {
                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 = 0; i < to.Length; i++)
                {
                    msg.To.Add(to[i]);
                }
                if (msg.To.Count <= 0) {
                    return;
                }
                msg.From = form;
                msg.Subject = subject;
                msg.Body = body;
                if (attachment!=null && !attachmentpath.Length.Equals(0))
                {
                    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;
            }
        }
    }