[Mimedefang] Exchange sends multipart/alternative instead of multipart/mixed

[Kenneth Porter]

I've encountered a 3-part message with the following header:

X-MimeOLE: Produced By Microsoft Exchange V6.5.7226.0

The message comprises 3 parts: A "look at this" message (text/plain, 
UTF-8), another message being forwarded (text/html, ISO-2022-jp), and a 
corporate disclaimer (text/plain, no charset specified). The package is 
sent within a multipart/alternative, which says that all 3 parts are 
supposed to be same content with different degrees of richness, best last, 
so Mozilla Thunderbird displays only the disclaimer. It lacks a UI to 
select other alternatives, so it's impossible to see the real meat of the 
message.

First, has anyone else seen this brain damage? Is it due to an Exchange 
misconfiguration? (Ie. can I recommend a specific action to the sender's IT 
department, short of replacing Exchange?)

Second, is it reasonable to fix this in MD by replacing 
multipart/alternative with multipart/mixed in the outermost Content-Type 
header?