异步，验证邮箱格式

          //使用异步
            delegate_Emailcom run = new delegate_Emailcom(Emailcom);
            IAsyncResult result = run.BeginInvoke(mailMessage, null, null);

private static readonly object SequenceLock = new object();
public delegate void delegate_Emailcom(MailMessage obj, string sjr);

    private void Emailcom(MailMessage obj,string sjr) 
    {
        lock (SequenceLock)
        {
                Regex r = new Regex("^\\s*([A-Za-z0-9_-]+(\\.\\w+)*@(\\w+\\.)+\\w{2,5})\\s*$");

                if (!r.IsMatch(sjr))
                {
                    textBox3.Text += $"{sjr}不是邮箱格式" + Environment.NewLine + Environment.NewLine;
                }
                else
                {
                obj.To.Add(new MailAddress(sjr.ToString()));
               }
                
        }
    }