[Alpine-info] Displaying Message/RFC822 attachments fails with IMAP

[Mark Crispin]

On Wed, 26 Nov 2008, Heikki Vesalainen / Ixonos wrote:

> I found the problem by comparing the BODYSTRUCTUREs to the results of the 

> imapd that comes with alpine. The _only_ thing "wrong" with the BODYSRUCTUREs 

> given by both my servers is that they are giving NIL as the 

> Content-Transfer-Encoding of the MESSAGE/RFC822 (it's the first NIL on the 

> third line in the example below, just before 1780).


That was one of the problems, yes.

Exchange is a hopeless case.  Microsoft told me that they have no 
intention of fixing the bugs in Exchange's IMAP server.


> I think alpine not tolerating the NIL is a problem in alpine.


That part of Alpine is functioning correctly.  See below.


> The 

> Content-Transfer-Encoding is not always present in MIME messages (AFAIK it's 

> not mandatory in MIME -- and should it be, that's besides the point since 

> most MUAs seem not to give it, the world is not perfect)


It's beside the point in another way as well.  MIME semantics do not 
dictate IMAP semantics.


> and as far as I 

> know, there is no specification that says that the IMAP server should 

> translate missing Content-Transfer-Encodings to "8BIT".


Since you got this far, I'll enlighten you the rest of the way.

The IMAP specification states that the encoding is mandatory (I should 
know, I wrote it).  NIL is prohibited in the encoding field of an IMAP 
body structure.

A reasonable server implementation will send the encoding as "8BIT" if the 
encapsulated message has any octets with values 0x80 or higher, and "7BIT" 
otherwise.

-- Mark --

http://panda.com/mrc
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Liberty is a well-armed sheep contesting the vote.