Can MailKit save a message to file?

[Axel D.]

Is your feature request related to a problem? Please describe.

The System.Net.Mail.SmtpClient class comes with a great feature that I need to perform automated tests: It can save messages to a pickup folder:

SmtpClient.DeliveryMethod = SmtpDeliveryMethod.SpecifiedPickupDirectory
SmtpClient.PickupDirectory = ...

Describe the solution you'd like

MailKit should be able to do so, too.

[Jeffrey Stedfast]

Based on Microsoft's referencesource, when SmtpDeliveryMethod.SpecifiedPickupDirectory is used, the SmtpClient saves the message to the specified pickup directory location using a randomly generated filename based on Guid.NewGuid ().ToString () + ".eml", so to achieve the same results with MailKit, you could do something like this:

public static void SaveToPickupDirectory (MimeMessage message, string pickupDirectory)
{
    do {
        // Generate a random file name to save the message to.
        var path = Path.Combine (pickupDirectory, Guid.NewGuid ().ToString () + ".eml");
        Stream stream;

        try {
            // Attempt to create the new file.
            stream = File.Open (path, FileMode.CreateNew);
        } catch (IOException) {
            // If the file already exists, try again with a new Guid.
            if (File.Exists (path))
                continue;

            // Otherwise, fail immediately since it probably means that there is
            // no graceful way to recover from this error.
            throw;
        }

        try {
            using (stream) {
                // IIS pickup directories expect the message to be "byte-stuffed"
                // which means that lines beginning with "." need to be escaped
                // by adding an extra "." to the beginning of the line.
                //
                // Use an SmtpDataFilter "byte-stuff" the message as it is written
                // to the file stream. This is the same process that an SmtpClient
                // would use when sending the message in a `DATA` command.
                using (var filtered = new FilteredStream (stream)) {
                    filtered.Add (new SmtpDataFilter ());

                    // Make sure to write the message in DOS (<CR><LF>) format.
                    var options = FormatOptions.Default.Clone ();
                    options.NewLineFormat = NewLineFormat.Dos;

                    message.WriteTo (options, filtered);
                    filtered.Flush ();
                    return;
                }
            }
        } catch {
            // An exception here probably means that the disk is full.
            //
            // Delete the file that was created above so that incomplete files are not
            // left behind for IIS to send accidentally.
            File.Delete (path);
            throw;
        }
    } while (true);
}

[Axel D.]

Excellent. Thanks a lot for this valuable answer!

PS: Wouldn't an information like this be valuable by being added to the MailKit documentation?

[Jeffrey Stedfast]

It's in the FAQ: https://github.com/jstedfast/MailKit/blob/master/FAQ.md#smtp-specified-pickup-directory

I couldn't figure out how to grab the link from my phone last night or I would have posted that :-)