ASP CDO issue with read receipt request

Question

I am have problems with an older classic ASP application where read receipts are employed in the code. This particular routine has been used for a number of years successfully but recently we have migrated to a new server with Windows 2008 r2, IIS 7.5 and SmarterMail 11.07 client. Now whenever the application attempts to send a server generated email, the SmarterMail logs are showing it successfully receives and authenticates the submission, but seems to terminate or abort the connection without cause and won't send the email without any errors. I'm at a loss here because like I stated, this routine has worked without problems for some time now and if we don't select the "read-receipt" option in the ASP application the email distributes just fine. I have included a shortened version of the code below and mainly looking for validation that the code for all intended purposes should work as is and if anyone may know of similar issues related to this within SmarterMail itself, like some kind of default security setting I am unaware of. Incidentally, if we manually use the SmarterMail webmail interface, we can successfully send mail with read receipts, so I know it should be possible. - Thank you kindly!

Code Example

    set Mail = Server.CreateObject("CDO.Message")

    'Basic configuration
    Mail.AutoGenerateTextBody = 0
    Mail.Configuration.Fields("http://schemas.microsoft.com/cdo/configuration/smtpserver") = strHost
    Mail.Configuration.Fields("http://schemas.microsoft.com/cdo/configuration/sendusing") = 2
    Mail.Configuration.Fields("http://schemas.microsoft.com/cdo/configuration/smtpserverport") = strPort
    Mail.Configuration.Fields.Update

    Mail.Fields("urn:schemas:mailheader:X-Mailer") = "Custom EMailer"
    Mail.Fields.update

    'Priority 
    Mail.Fields("urn:schemas:mailheader:X-Priority") = emPriority  
    Mail.Fields("urn:schemas:mailheader:X-MSMail-Priority") = emPriorityTxt  
    Mail.Fields("urn:schemas:httpmail:importance") = emPriority  
    Mail.Fields.update

    'Addressing
    With Mail
      .From = strFrom
      .ReplyTo = strReplyTo
      .To = strTo
      .CC = strCc
      .BCC = strBCc
    End With

    'Attachments
    if len(sfls) > 0 then
      if instr(1,sfls,",",1) > 0 then
        strAttachments = split(sfls,",",-1,1)
      else
        strAttachments = sfls
      end if

      if isarray(strAttachments) then
        for x = 0 to ubound(strAttachments)
          Mail.AddAttachment strAttachments(x)
        next
      else
        Mail.AddAttachment strAttachments
      end if
    end if

    'Body
    Mail.Subject = strSubject
    if isHTML then
      Mail.HTMLBody = strBody
    else
      Mail.TextBody = strBodyTxt
    end if

    '###################################################################
    'If this section is included the email will not send, times out or 
    'connection is terminated, according to the SmarterMail logs
    '###################################################################
    ' Read/Delivery Receipt
    if isRead then
      Mail.Fields("urn:schemas:mailheader:disposition-notification-to") = rrReplyTo
      Mail.Fields("urn:schemas:mailheader:return-receipt-to") = rrReplyTo  
      Mail.DSNOptions = 14
      Mail.Fields.Update
    end if
    '###################################################################

    'Send Message
    strErr = ""
    bSuccess = False
    On Error Resume Next
    Mail.Send
    If Err <> 0 Then
      strErr = Err.Description
    else
      bSuccess = True
    End If

    set Mail = nothing

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