[mew-int 2477] Re: Mew not recognising some attachments

[Harald Hanche-Olsen]

+ Gernot Heiser <gernot at example.com>:

> I get this problem frequently with people sending me mails with
> attachments from Macs. Mew only shows the main body of the mail, but
> not the attachments. metamail usually manages to attract them, so they
> don't seem ill-formed.
> 
> I tried to attach an example mail, but that exceeded the size limit of
> the mailing list, so it was blocked waiting moderator approval, which
> never came until the post expired. Ask me if you want the example.

This is a very familiar problem, and arguably a bug in Apple
Mail. What the program typically does is to send the mail as the type
Multipart/Alternative with a structure like the following (this is
from an actual email I received yesterday):

Q    1  Text/Plain(ISO-8859-1)*
Q    2.1  Text/Html(ISO-8859-1)
B    2.2  Application/Pdf
     2.3  Text/Html(US-ASCII)
B    2.4  Application/Pdf
     2.5  Text/Html(US-ASCII)

Now, the meaning of Multipart/Alternative is supposed to be that the
two parts are completely equivalent, in the sense that they both
contain the same information, but presented differently.  This is
commonly done with Text/Plain and Text/Html:  Text based email
programs will choose the former, while email programs that are HTML
capable will pick the latter.

In the above example the second alternative part of the email is
itself a multipart message, this time Multipart/Mixed: Its five parts
2.1-2.5 are indeed of mixed type: HTML and PDF.  In effect, Apple Mail
lied when it claimed that part 2 is just a different version of part
1, since part 1 is missing the PDF files.

Appropriately, the above mail should have been packaged as one
Multipart/Mixed, organized as

     1.1  Text/Plain
     1.2  Text/Html
     2  Application/Pdf
     3  Application/Pdf

with part 1 being a Multipart/Alternative.

It's all very annoying.  Use the colon key (:) to force mew to show
all the parts of a Multipart/Alternative message.

You know you may have this happening when you see this header line:

X-Mew: Text/Plain in Multipart/Alternative as a singlepart

- Harald