尝试连接到“smtp.office365.com”时收到 MailKit.Security.SslHandshakeException

Question

我正在尝试使用 MailKit 通过“smtp.office365.com”发送电子邮件。这是我正在使用的代码。

using (var client = new SmtpClient(new ProtocolLogger("smtp.log")))
{
    client.ServerCertificateValidationCallback = (s, c, h, e) => true;
    client.Connect("smtp.office365.com", 587, SecureSocketOptions.SslOnConnect);
    client.Authenticate(new SaslMechanismNtlmIntegrated());
    Debug.WriteLine(client.IsAuthenticated);
    client.Send(message);
    client.Disconnect(true);
}

我从 GitHub 上的 this comment 获得的 SaslMechanismNtlmIntegrated 类。

每当我运行这段代码时，我都会收到一个SslHandshakeException。

以下是异常的详细信息：

MailKit.Security.SslHandshakeException
  HResult=0x80131500
  Message=An error occurred while attempting to establish an SSL or TLS connection.

One possibility is that you are trying to connect to a port which does not support SSL/TLS.

The other possibility is that the SSL certificate presented by the server is not trusted by the system for one or more of the following reasons:
1. The server is using a self-signed certificate which cannot be verified.
2. The local system is missing a Root or Intermediate certificate needed to verify the server's certificate.
3. The certificate presented by the server is expired or invalid.

See https://github.com/jstedfast/MailKit/blob/master/FAQ.md#InvalidSslCertificate for possible solutions.
  Source=MailKit
  StackTrace:
   at MailKit.Net.Smtp.SmtpClient.<ConnectAsync>d__70.MoveNext()
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at MailKit.Net.Smtp.SmtpClient.Connect(String host, Int32 port, SecureSocketOptions options, CancellationToken cancellationToken)
   at QuoteAndOrder.SpecialsQuoteWindow.BtnEmail_Click(Object sender, RoutedEventArgs e) in SpecialsQuoteWindow.xaml.cs:line 501

Inner Exception 1:
IOException: The handshake failed due to an unexpected packet format.

我去了详细信息中提到的FAQ，但给出的解决方法并没有解决问题。

Answer 1

willaien 提到的解决方案解决了这个问题。即，使用SecureSocketOptions.StartTls 而不是SecureSocketOptions.SslOnConnect。