(.NET Core C#) Processing a multipart/report Delivery Status Notification (Bounce Notification)

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This example discusses the format of Delivery Status Notification emails and how to process them.

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// Here are the MIME structures, showing the content-type and nesting of the MIME parts of three sample
// multipart/report DSN (Delivery Status Notification) emails.

// This 1st sample includes a "text/rfc822-headers" MIME subpart. 

// multipart/report
//     text/plain
//     message/delivery-status
//     text/rfc822-headers
//     message/rfc822

// This 2nd sample lacks the text/rfc-headers part, but the "report type" information
// is offered in both plain-text and HTML formats.

// multipart/report
//     multipart/alternative
//         text/plain
//         text/html
//     message/delivery-status
//     message/rfc822

// ----------------------------------------------------------------------------------------------------

// A multipart/report MIME delivery status notification follows a specific format defined by the Internet Engineering Task Force (IETF) in RFC 3464, 
// which outlines the "An Extensible Message Format for Delivery Status Notifications" standard. The format consists of multiple parts within a 
// multipart/report structure. Here's an overview of the main parts involved:
// 
// The 1st sub-part under multipart/report is the body of the DSN to be displayed by the email client (such as Outlook).
// It can be a simple text/plain body, or it can be multipart/alternative and offer a few alternative format, typically plain-text and HTML.
// HTML is best for viewing a program such as Outlook. 
// This part of the multipart/report is not structured for programmatic processing.  It's meant to be viewed by a human.

// --------------------
// The "message/delivery-status" part within a multipart/report MIME structure follows a specific format to provide details about the delivery status
// of an email message.  Here's an overview of the format and the key components within the "message/delivery-status" part:
// 
// (1) Content-Type and Reporting-UA:
// The "message/delivery-status" part begins with the Content-Type header specifying "message/delivery-status". 
// It may also include a Reporting-UA (Reporting User Agent) field that identifies the software or system generating the delivery status notification.
// 
// For example:
// 
// Content-Type: message/delivery-status
// Reporting-UA: Example Mail System 1.0
// 
// (2) Fields:
// The "message/delivery-status" part contains a series of fields, each providing specific information about the delivery status. 
// These fields are structured as key-value pairs.
// 
// Common fields include:
// 
//     Final-Recipient: Specifies the recipient for whom the delivery status is being reported.
//     Action: Describes the action performed by the reporting system (e.g., failed, delivered, delayed, etc.).
//     Status: Indicates the status code or reason for the delivery attempt result.
//     Remote-MTA: Specifies the host or system that attempted the delivery.
//     Diagnostic-Code: Provides additional diagnostic information, such as error codes or explanations.
// 
// For example:
// 
// Final-Recipient: rfc822; john.doe@example.com
// Action: failed
// Status: 5.1.1
// Remote-MTA: smtp.example.com
// Diagnostic-Code: smtp; 550 Requested action not taken: mailbox unavailable
// 
// (3) Additional Fields:
// Additional fields may be included in the "message/delivery-status" part to provide further information about the delivery attempt. 
// These fields can vary depending on the implementation or specific needs of the system generating the delivery status notification.
// For example:
// 
// X-Spam-Flag: YES
// X-Spam-Score: 7.2
// 
// Note: The specific fields and their values within the "message/delivery-status" part can vary depending on the implementation
// or the email server/application generating the delivery status notification. The structure described above represents the standard format
// as defined in RFC 3464, but variations may exist in practice.

// --------------------

// The "text/rfc822-headers" MIME part, if included, contains the headers of the original email message
// for which the delivery status notification is being generated. It provides a subset of the headers from the original message,
// typically excluding the message body and attachments.
// 
// The purpose of including the "text/rfc822-headers" part is to provide contextual information about the original message.
// It allows the recipient to review the original headers, such as the subject, sender, recipients, date, and other relevant information,
// in order to understand the context and details of the email message for which the delivery status notification is being generated.
// 
// Note that the specific headers included in the "text/rfc822-headers" part can vary based on the implementation or requirements
// of the system generating the delivery status notification.

// --------------------

// If the message/rfc822 part is present, it contains the full MIME of the email that was not delivered.
// In Chilkat terminology, this is an attached message.

// OK, let's write code to process a multipart/report email.
bool success;

Chilkat.Email email = new Chilkat.Email();
success = email.LoadEml("qa_data/eml/deliveryStatus.eml");
// success = email.LoadEml("qa_data/eml/sample_multipart_report.eml");
if (success == false) {
    Debug.WriteLine(email.LastErrorText);
    return;
}

// Verify this is a multipart/report email..
if (email.IsMultipartReport() == false) {
    Debug.WriteLine("Not a multipart/report email.");
    return;
}

// Get the body that is to be displayed to a human in an email program (such as Outlook).
if (email.HasPlainTextBody() == true) {
    Debug.WriteLine("Plain text body:");
    // println email.GetPlainTextBody();
}
else {
    if (email.HasHtmlBody() == true) {
        // Convert HTML to plain-text..
        Chilkat.HtmlToText h2t = new Chilkat.HtmlToText();
        Debug.WriteLine("HTML body converted to plain-text:");
        Debug.WriteLine(h2t.ToText(email.GetHtmlBody()));
    }
    else {
        Debug.WriteLine("Has no plain-text or HTML body...");
    }

}

Debug.WriteLine("---------------------------------");

// Now get information from the message/delivery-status part (or the message/disposition-notification part)
Debug.WriteLine("--- Delivery Status Information:");
Debug.WriteLine("Status: " + email.GetDeliveryStatusInfo("Status"));
Debug.WriteLine("Action: " + email.GetDeliveryStatusInfo("Action"));
Debug.WriteLine("Reporting-MTA: " + email.GetDeliveryStatusInfo("Reporting-MTA"));

Chilkat.StringArray sa = email.GetDsnFinalRecipients();
int numFinalRecipients = sa.Count;
int i = 0;
while (i < numFinalRecipients) {
    Debug.WriteLine("final recipient: " + sa.GetString(i));
    i = i + 1;
}

Debug.WriteLine("---------------------------------");

// If the multipart/report contains a text/rfc822-headers, it can be retrieved like this:
string headersText = email.GetNthTextPartOfType(0,"text/rfc822-headers",false,false);
if (email.LastMethodSuccess == true) {
    Debug.WriteLine("The text/rfc822-headers part exists..");
    Debug.WriteLine("");
    Debug.WriteLine(headersText);

    // If you wish to process the headers, you can load them into a MIME object and use the Chilkat MIME functionality to examine the headers.
    Chilkat.Mime mime = new Chilkat.Mime();
    mime.LoadMime(headersText);

    // Do whatever you want.. 
    // For example, look at the "To" header.
    Debug.WriteLine("MIME To header:");
    Debug.WriteLine(mime.GetHeaderField("To"));
}

Debug.WriteLine("---------------------------------");

// Finally, if the original email was attached, you can load it into another Chilkat Email object instance and
// do what you want with it..

if (email.NumAttachedMessages > 0) {
    // Get the 1st attachment message (assume we don't have more than one attached message)
    Chilkat.Email origEmail = email.GetAttachedMessage(0);
    if (email.LastMethodSuccess == true) {
        Debug.WriteLine("Attached message subject: " + origEmail.Subject);
        // Do whatever else you want..

    }

}