(Go) 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.
    var success bool

    email := chilkat.NewEmail()
    success = email.LoadEml("qa_data/eml/deliveryStatus.eml")
    // success = email.LoadEml("qa_data/eml/sample_multipart_report.eml");
    if success == false {
        fmt.Println(email.LastErrorText())
        email.DisposeEmail()
        return
    }

    // Verify this is a multipart/report email..
    if email.IsMultipartReport() == false {
        fmt.Println("Not a multipart/report email.")
        email.DisposeEmail()
        return
    }

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

    }

    fmt.Println("---------------------------------")

    // Now get information from the message/delivery-status part (or the message/disposition-notification part)
    fmt.Println("--- Delivery Status Information:")
    fmt.Println("Status: ", *email.GetDeliveryStatusInfo("Status"))
    fmt.Println("Action: ", *email.GetDeliveryStatusInfo("Action"))
    fmt.Println("Reporting-MTA: ", *email.GetDeliveryStatusInfo("Reporting-MTA"))

    sa := email.GetDsnFinalRecipients()
    numFinalRecipients := sa.Count()
    i := 0
    for i < numFinalRecipients {
        fmt.Println("final recipient: ", *sa.GetString(i))
        i = i + 1
    }

    sa.DisposeStringArray()

    fmt.Println("---------------------------------")

    // If the multipart/report contains a text/rfc822-headers, it can be retrieved like this:
    headersText := email.GetNthTextPartOfType(0,"text/rfc822-headers",false,false)
    if email.LastMethodSuccess() == true {
        fmt.Println("The text/rfc822-headers part exists..")
        fmt.Println("")
        fmt.Println(*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.
        mime := chilkat.NewMime()
        mime.LoadMime(*headersText)

        // Do whatever you want.. 
        // For example, look at the "To" header.
        fmt.Println("MIME To header:")
        fmt.Println(*mime.GetHeaderField("To"))
    }

    fmt.Println("---------------------------------")

    // 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)
        origEmail := email.GetAttachedMessage(0)
        if email.LastMethodSuccess() == true {
            fmt.Println("Attached message subject: ", origEmail.Subject())
            // Do whatever else you want..
            origEmail.DisposeEmail()
        }

    }


    email.DisposeEmail()
    h2t.DisposeHtmlToText()
    mime.DisposeMime()