Duplicate of Ticket #9827.

Hum, indeed, the messages are badly formatted.
Actually Thunderbird displays the bmp inline, the pps is displayed as attach..
But hey, if the message is not in the correct format, the client 
behavior is also "unexpected".

For the record, it appears that what was intended was this:

multipart/alternative
   text/plain
   text/html
   image/bmp

In other words, show the image if possible but if not then show 
placeholder text that says that an image is attached.  Still not 
tremendously useful.

Thinking about this a bit more... I would not be opposed to outputting 
a status message saying there are message parts contained within a 
multipart/related part that can not be accessed via the base related 
part.  Although I'm not sure how easy this would be.

Thunderbird is buggy then.  There is no attachment in either message.

This is what the MIME structure looks like for the BMP message:

multipart/related
   multipart/alternative
     text/plain
     text/html
   image/bmp

The image/bmp MUST somehow be referred to in either text/plain or 
text/html (the "root" part of the multipart/alternative).  The whole 
point of multipart/related is that the ENTIRE part can be represented 
in a single data object.  multipart/related does not allow attachments 
inside of it - that simply doesn't make any sense.

If Thunderbird is showing this part, its attachment recognition 
algorithm is badly broken (which is true, as previously mentioned when 
discussing forwarding).

Attached two messages, one with a pps and the other with a bmp, that 
display correctly on Thunderbird, but Horde doesn't.