I have a lovely script which is working great at the moment with AppleScript and Outlook.
tell application "Microsoft Outlook"
set selected_folder_name to name of selected folder
set selected_mail to messages of mail folder selected_folder_name
-- this line replaces a tonne of other text, it's for simplisticty only
set msg to item 1 of selected_mail as text
set msgContent to content of msg as text
if msgContent contains "</html>" then
tell application "Finder"
set msgContentSnipped to text 1 thru ((offset of "/body" in msgContent) - 2) of msgContent
end tell
set pPosixPath to (the POSIX path of prePos) as text
set msgContentFinal to msgContentSnipped & "<B>Trust No One: They are all watching you!</B></BODY></HTML>"
set content of msg to msgContentFinal
end if
end tell
I’ve stuck most of it here as I believe in giving back to the community 
Anyways…
I know that Outlook 2011 supports content type of text also
I haven’t found a way to detect the content type of an email. I suppose if the email content DOESN’T content then you know it’s text? I’d rather do something a little less, well, fudgey