MS Outlook: Dumping MIME EML Email Files for Spamassassin Training

Here’s a VBA script that I’m using to train Spamassassin from Outlook. It saves out email messages to a file server where messages are used to train the filter. The problem here is that Outlook doesn’t save EML (MIME format) files. You can save messages as text, but lately, spammers have been loading messages with a lot of chaff text that looks like regular email. You can’t train with that, because it might cause the filter to start mis-identifying legit email as spam.

The chaff is usually in the HTML as white text, at a small font size. So the user never sees it, but the filter’s supposed to see it.

The partial solution is to save the messages as regular email, and .EML file, with the HTML parts intact. Spamassassin seems to have code that will treat obfuscated HTML correctly. That way, the white text is removed from the training.

This code is very raw. Plenty of things to fix, like error handling, but it is working right now. The code is set up not to save out text versions of the email.

To use it, go to a folder, select the spam, and run the MarkAsSpam macro.

This is intended to be used by the sysadmin. I have learned that end-user spam filtering is hit and miss. Some people use spam filters to block legit email rather than unsubscribe from the messages.

Sub MarkAsHam()
    CopyMessagesToFile ("\mailfilterspamassassin-ham")
End Sub

Sub MarkAsSpam()
    CopyMessagesToFile ("\mailfilterspamassassin-spam")
End Sub

' Move the selected message(s) to the given folder **************************
Function CopyMessagesToFile(folderName As String)

    Dim myOLApp As Application
    Dim myNameSpace As NameSpace
    Dim myInbox As MAPIFolder
    Dim currentMessage As MailItem
    Dim errorReport As String
    Set myOLApp = CreateObject("Outlook.Application")
    Set myNameSpace = myOLApp.GetNamespace("MAPI")
    Set myInbox = myNameSpace.GetDefaultFolder(olFolderInbox)

    ' Figure out if the active window is a list of messages or one message
    ' in its own window
    On Error GoTo QuitIfError    ' But if there's a problem, skip it
    Select Case myOLApp.ActiveWindow.Class
        ' The active window is a list of messages (folder); this means there
        ' might be several selected messages
        Case olExplorer
            Debug.Print "list of messages"
            For Each currentMessage In myOLApp.ActiveExplorer.Selection
                Call writeAsFile(folderName, currentMessage)
        ' The active window is a message window, meaning there will only
        ' be one selected message (the one in this window)
        Case olInspector
            Call writeAsFile(folderName, myOLApp.ActiveInspector.CurrentItem)
        ' can't handle any other kind of window; anything else will be ignored
    End Select
QuitIfError:       ' Come here if there was some kind of problem
    Set myOLApp = Nothing
    Set myNameSpace = Nothing
    Set myInbox = Nothing
    Set currentMessage = Nothing
End Function

Sub writeAsFile(folderName As String, item As MailItem)
    On Error GoTo Bail
    Dim x As MailItem
    Dim fn As String
    Set x = item
    'Let fn = folderName & Right(x.EntryID, 64) & ".txt"
    'Debug.Print "file will be " & fn
    'Open fn For Output As #1
    '    Print #1, "From : " & x.SenderEmailAddress
    '    Print #1, "To: " & x.To
    '    Print #1, "Subject: " & x.Subject
    '    Print #1, vbCrLf & vbCrLf
    '    Print #1, x.body
    Let fn = folderName & Right(x.EntryID, 64) & ".eml"
    Debug.Print "file will be " & fn
    Open fn For Output As #2
        Print #2, "From : " & x.SenderEmailAddress
        Print #2, "To: " & x.To
        Print #2, "Subject: " & x.Subject
        Print #2, "MIME-Version: 1.0"
        Print #2, "Content-Type: multipart/alternative;"
        Print #2, "        boundary = ""----=_NextPart_000_000D_01CCF6AD.D1159750"""
        Print #2, "Content-Language: en-us"
        Print #2, ""
        Print #2, "This is a multipart message in MIME format."
        Print #2, ""
        Print #2, "------=_NextPart_000_000D_01CCF6AD.D1159750"
        Print #2, "Content-Type: text/plain;"
        Print #2, "        Charset = ""us-ascii"""
        Print #2, "Content-Transfer-Encoding: 7bit"
        Print #2, ""
        Print #2, item.body
        Print #2, "------=_NextPart_000_000D_01CCF6AD.D1159750"
        Print #2, "Content-Type: text/html;"
        Print #2, "        Charset = ""UTF-8"""
        Print #2, "Content-Transfer-Encoding: 7-bit"
        Print #2, "Content-Disposition: inline"
        Print #2, ""
        Print #2, item.HTMLBody
        Print #2, "------=_NextPart_000_000D_01CCF6AD.D1159750--"
    On Error GoTo 0

    Close #1
    Close #2
    Set item = Nothing
End Sub