SMTP sendmail挂起没有任何错误，我们的响应

我使用SmtpClient发送电子邮件与附件。发送电子邮件的方法在

下面

  public static void SendEmail(string subject, string messageBody, string toEmailId, List<string> attachments=null, List<string> cc = null, bool IsBodyHtml = false)
    {
        try
        {
            var fromAddress = new MailAddress("email@email.com");
            var toAddress = new MailAddress(toEmailId);
            const string fromPassword = "password";

            var smtp = new SmtpClient
            {
                Host = "smtp.gmail.com",
                Port = 587,
                EnableSsl = true,
                DeliveryMethod = SmtpDeliveryMethod.Network,
                UseDefaultCredentials = false,
                Credentials = new NetworkCredential(fromAddress.Address, fromPassword),
                Timeout= 1000 * 60
            };

            using (var message = new MailMessage(fromAddress, toAddress)
            {
                Subject = subject,
                Body = messageBody,
                IsBodyHtml = IsBodyHtml

            })
            {
                if (cc != null)
                {
                    foreach (string s in cc)
                        message.CC.Add(s);
                }
                if (attachments != null)
                {
                    foreach (string attachment in attachments)
                    {
                        message.Attachments.Add(new Attachment(attachment));
                    }
                }

                Console.WriteLine("email sending");
                smtp.Send(message);
                //Clean up attachments
                foreach (Attachment attachment in message.Attachments)
                {
                    attachment.Dispose();
                }
            }
        }
        catch (Exception ex)
        {
            throw ex;
        }
    }

我能够发送没有附件的电子邮件与上述SMTP配置。但是当我使用附件时，程序在smtp.Send(message)之后挂起，没有给出任何响应/错误。

相同的代码在我的本地机器上运行良好，但当我将其上传到服务器并运行时，它不响应。我也在服务器上尝试了以下步骤。

1. 在服务器上打开587端口。
2. 给附件文件夹所有权限。