Modify contents of incoming email in Outlook 2011 for Mac

Question

I'm trying to modify an incoming email in Outlook 2011 for Mac using IMAP.

The algorithm is as follows:

1. Get the source(raw text) of incoming message
2. Write it to HTML file
3. Modify the HTML file through a Python script
4. Write back to Outlook email (this is where I'm facing a problem)

I'm not able to write back the HTML file to incoming email. What am I missing here? My code is here for your reference:

set urtext to string
set fileContents to string
tell application "Microsoft Outlook"
    set theMessage to item 1 of (get current messages)
    set urtext to source of theMessage
end tell

--write source to the file
set newFile to "/Users/mymac/Desktop/newTest1.html"
set eof of newFile to 0
open for access newFile with write permission
write urtext to newFile
close access newFile

--modifying the contents of the email
do shell script "/Users/mymac/Documents/'Microsoft User Data'/'Outlook Script 
Menu Items'/test.py"

--read source from the file
set theFile to "/Users/mymac/Desktop/output3.html"
open for access theFile
set fileContents to (read theFile)
close access theFile

--problem here: how to write the source to the existing viewed message in 
-- the main window without duplications
tell application "Microsoft Outlook"
    set the_messages to selection
    repeat with this_message in the_messages

    --the line below modifies the contents, but I get two incoming mail messages
    --[one modified and one unmodified]
    set theMessage to make incoming message with properties {source:fileContents}

    --the line below does not modify the source of the message in view pane,
    --It gives an error 'Microsoft Outlook got an Errror: Applevent Handler Failed
    --set source of this_message to fileContents 

    end repeat 
end tell

Can this be done? Is there any other way whereby I can modify the contents of incoming message through Cocoa/Spamseive or creating a manual filter between the Exchange server and Outlook 2011 to do this process?