(Visual Basic 6.0) 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.
Dim success As Long

Dim email As New ChilkatEmail
success = email.LoadEml("qa_data/eml/deliveryStatus.eml")
' success = email.LoadEml("qa_data/eml/sample_multipart_report.eml");
If (success = 0) Then
    Debug.Print email.LastErrorText
    Exit Sub
End If

' Verify this is a multipart/report email..
If (email.IsMultipartReport() = 0) Then
    Debug.Print "Not a multipart/report email."
    Exit Sub
End If

' Get the body that is to be displayed to a human in an email program (such as Outlook).
If (email.HasPlainTextBody() = 1) Then
    Debug.Print "Plain text body:"
    ' println email.GetPlainTextBody();
Else
    If (email.HasHtmlBody() = 1) Then
        ' Convert HTML to plain-text..
        Dim h2t As New HtmlToText
        Debug.Print "HTML body converted to plain-text:"
        Debug.Print h2t.ToText(email.GetHtmlBody())
    Else
        Debug.Print "Has no plain-text or HTML body..."
    End If

End If

Debug.Print "---------------------------------"

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

Dim sa As CkStringArray
Set sa = email.GetDsnFinalRecipients()
Dim numFinalRecipients As Long
numFinalRecipients = sa.Count
Dim i As Long
i = 0
Do While i < numFinalRecipients
    Debug.Print "final recipient: " & sa.GetString(i)
    i = i + 1
Loop

Debug.Print "---------------------------------"

' If the multipart/report contains a text/rfc822-headers, it can be retrieved like this:
Dim headersText As String
headersText = email.GetNthTextPartOfType(0,"text/rfc822-headers",0,0)
If (email.LastMethodSuccess = 1) Then
    Debug.Print "The text/rfc822-headers part exists.."
    Debug.Print ""
    Debug.Print 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.
    Dim mime As New ChilkatMime
    success = mime.LoadMime(headersText)

    ' Do whatever you want.. 
    ' For example, look at the "To" header.
    Debug.Print "MIME To header:"
    Debug.Print mime.GetHeaderField("To")
End If

Debug.Print "---------------------------------"

' 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) Then
    ' Get the 1st attachment message (assume we don't have more than one attached message)
    Dim origEmail As ChilkatEmail
    Set origEmail = email.GetAttachedMessage(0)
    If (email.LastMethodSuccess = 1) Then
        Debug.Print "Attached message subject: " & origEmail.Subject
        ' Do whatever else you want..

    End If

End If