查找導致異常的確切原因-System.Net.Sockets.SocketException

Question

我嘗試使用下面給出的代碼將郵件發送到SMTP郵件服務器。 但是，我遇到一個錯誤-

Error: System.Reflection.TargetInvocationException: Exception has 
been thrown by the target of an invocation. ---> System.Net.Mail.SmtpException:
Failure sending mail. ---> System.Net.WebException: Unable to connect to
the remote server ---> System.Net.Sockets.SocketException: A connection 
attempt failed because the connected party did not properly respond after 
a period of time, or established connection failed because connected host 
has failed to respond 123.456.789:587
at System.Net.Sockets.Socket.DoConnect(EndPoint endPointSnapshot, 
SocketAddress socketAddress)
at System.Net.ServicePoint.ConnectSocketInternal(Boolean connectFailure, 
Socket s4, Socket s6, Socket& socket, IPAddress& address, ConnectSocketState 
state, IAsyncResult asyncResult, Int32 timeout, Exception& exception)

此異常告訴我可能的原因列表-連接嘗試失敗，因為一段時間后連接方未正確響應，或者連接建立失敗，因為連接的主機未能響應123.456.789：587

但這並不能告訴我原因到底是什么-端口號，錯誤的用戶名，密碼或其他原因。 我如何找出確切原因。

這是我使用的代碼- 從C＃發送帶有附件的電子郵件，附件作為Thunderbird中的第1.2部分到達

using System.Net;
using System.Net.Mail;

public void email_send()
{
    MailMessage mail = new MailMessage();
    SmtpClient SmtpServer = new SmtpClient("smtp.gmail.com");
    mail.From = new MailAddress("your mail@gmail.com");
    mail.To.Add("to_mail@gmail.com");
    mail.Subject = "Test Mail - 1";
    mail.Body = "mail with attachment";

    System.Net.Mail.Attachment attachment;
    attachment = new System.Net.Mail.Attachment("c:/textfile.txt");
    mail.Attachments.Add(attachment);

    SmtpServer.Port = 587;
    SmtpServer.Credentials = new System.Net.NetworkCredential("your 
    mail@gmail.com", "your password");
    SmtpServer.EnableSsl = true;

    SmtpServer.Send(mail);

}

Answer 1

該IP地址顯然不正確123.456.789:587 。
在命令提示符下嘗試ping smtp.gmail.com ，以查看它是否解析到該地址。 如果是這樣，則可以在hosts文件（C：\\ Windows \\ System32 \\ drivers \\ etc \\ hosts）中的某個位置覆蓋該值。

運行您的代碼段后，但隨后我立即從Google處收到了“阻止登錄嘗試”的通知，因為這種身份驗證方法顯然不符合其當前標准。