[Mailman-Users] Extra space in mime encoded headers

Mark Sapiro mark at msapiro.net
Sat Oct 3 21:59:18 CEST 2009

Oliver Betz wrote:
>describes a bug I'm suffering from: MIME encoded headers are re-
>encoded by mailman and spaces are added around each encoded 

If clients encoded the entire word instead of just single characters,
this wouldn't be an issue. I believe most clients do this, and I think
RFC 2047 effectively requires it.

The example problem header from the bug report is

Subject: abcd=?iso-8859-1?q?=e4?=ttt

RFC 2047 section 2 contains the following statement

 IMPORTANT: 'encoded-word's are designed to be recognized as 'atom's
 by an RFC 822 parser. 

In the above subject header, the encoded-word is =?iso-8859-1?q?= and
it is not an atom because atoms are delimited by white space.

Thus, this encoding is simply wrong, and it is the generating MUA that
is at fault.

>The affected mailman installation is 2.1.5 and maintained by a 
>hoster, not myself. Therefore I would like to know what to tell the 
>I couldn't find the bug in the mailman (Launchpad) bug tracker so I 
>wonder whether this bug is known to the developers and whether it's 
>fixed now.

The 'problem' still exists in some configurations. The underlying issue
is in the Python email.Header module. Current versions of the Python
email package from Python 2.5 and later will not parse the above
subject as containing an encoded-word at all, and a Mailman using one
of these email packages will probably just output that Subject: string

Older versions of the email package parse that Subject: into three
parts; 'abcd', the encoded word '=?iso-8859-1?q?=e4?=' and 'ttt'.
Then, when these pieces are reassembled the encoded word is properly
delimited by spaces, thus introducing the extra spaces you see.

This is complicated by the fact that prior to 2.1.12, Mailman used it's
own version of the email package instead of the underlying Python
version. Thus, you will see this problem behavior with Mailman 2.1.11
and before regardless of the Python version and also with Mailman
2.1.12 if the underlying Python is 2.4.x, but not with Mailman 2.1.12
if the underlying Python is 2.5 or newer.

Mark Sapiro <mark at msapiro.net>        The highway is for gamblers,
San Francisco Bay Area, California    better use your sense - B. Dylan

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