[MacOSX] SmtpCommandException: ITMIME

[ghost]

• What were you trying to do?

Trying to send a sample email to a local SMTP server called Smtp4dev on Mac OS X 10.13.3 with .Net Core 2.0.

Gets to the part where it tries to send FROM: information, and I believe the issue could be centered around carriage / newline characters.

Sample code:

var message = new MimeMessage ();
message.From.Add (new MailboxAddress ("Joey Tribbiani", "joey@friends.com"));
message.To.Add (new MailboxAddress ("Mrs. Chanandler Bong", "chandler@friends.com"));
message.Subject = "How you doin'?";

message.Body = new TextPart ("plain") {
    Text = @"Hey Chandler,

    I just wanted to let you know that Monica and I were going to go play some paintball, you in?

    -- Joey"
};

using (var client = new SmtpClient (new ProtocolLogger ("smtp.log"))) {
    // For demo-purposes, accept all SSL certificates (in case the server supports STARTTLS)
    client.ServerCertificateValidationCallback = (s,c,h,e) => true;

    client.Connect ("localhost", 2525, false);

    client.Send (message);
    client.Disconnect (true);
}

Reason I posted up this sample email is because it wasn't working with my company's app on my computer, but a coworker had the same project working fine on windows. So I launched up this sample program using the same Mailkit package and received the exact error here.

Thought it could be because of Smtp4dev but I can load up a MailMessage() email and send using System.Net.Mail.SmtpClient and that works fine with Smtp4dev.

• What happened?

Unhandled Exception: MailKit.Net.Smtp.SmtpCommandException: ITMIME
   at MailKit.Net.Smtp.SmtpClient.ProcessMailFromResponse(MimeMessage message, MailboxAddress mailbox, SmtpResponse response)
   at MailKit.Net.Smtp.SmtpClient.<MailFromAsync>d__88.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at MailKit.Net.Smtp.SmtpClient.<SendAsync>d__99.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at MailKit.Net.Smtp.SmtpClient.<SendAsync>d__99.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at MailKit.Net.Smtp.SmtpClient.Send(FormatOptions options, MimeMessage message, CancellationToken cancellationToken, ITransferProgress progress)
   at MailKit.MailTransport.Send(MimeMessage message, CancellationToken cancellationToken, ITransferProgress progress)
   at ConsoleApp1.Program.Main(String[] args) in /Users/anthonyronning/Dev/Projects/TestEmail/ConsoleApp1/ConsoleApp1/Program.cs:line 55

Line 55 is client.Send (message);

• Step-by-step reproduction instructions and/or a simple test case.
  1. Load up https://github.com/rnwood/smtp4dev and follow the few instructions needed to get it up and running. I launched with command ASPNETCORE_URLS="http://0.0.0.0:5001" dotnet Rnwood.Smtp4dev.dll to change hosting ports and changed smtp port to 2525 in the appsettings.json
  2. Load up sample email program with any .Net based IDE (I tried Rider, Visual Studio, and VSCode - all same error).
  3. Run program and view error.

Below is the SMTP log:

Connected to smtp://localhost:2525/?starttls=when-available
S: 220 ip-***-***-***-*** smtp4dev ready
C: EHLO [127.0.0.1]
S: 250 Nice to meet you.
S: 8BITMIME
S: SIZE
C: MAIL FROM:<joey@friends.com>
C: RSET

The reponse coming back after the MAIL FROM is ITMIME with a code of 8. Not sure where this comes from, doesn't look like something called out anywhere in Smtp4dev code.

[jstedfast]

The problem is with Smtp4dev which is sending invalid responses.

Note the 8BITMIME line. That's the problem right there. The reason it's a problem is because it is supposed to start with a SMTP response code, but it doesn't.

The previous line (the response to the EHLO command) should also be changed and the entire EHLO response should look like this:

250-Nice to meet you.
250-8BITMIME
250 SIZE

The - character immediately following the 250 means that there is at least 1 more line of the response that the client needs to read.

File a bug against Smtp4dev.