/// <summary>
 /// 生成SMTP客户端
 /// </summary>
 protected virtual SmtpClient BuildSmtpClient() => _smtpBuilder.Build();
 /// <summary>
 /// 生成SMTP客户端
 /// </summary>
 /// <returns></returns>
 protected virtual SmtpClient BuildSmtpClient()
 {
     return(_smtpBuilder.Build());
 }