#<buffer *nntpd*> and split-fancy-:-unparseable base64-encoded header.

[Garreau\, Alexandre]

I am unsure if this is an appropriate and well-descriptive subject for
this issue, please point it out to me otherwise.

I am currently splitting my mail with nnmail-split-fancy’s :, according
list-id content, and recently I noticed I got a lot of mail in garbage
directories named with long base64 strings: I then experimentally
noticed the buffer nnmail-split-fancy’s : acts on is still
base-64-encoded for utf-8 content.  However some mailing-list of online
(but graded) course of my college must have something wrong because
since the description of its list-id is in utf-8, the list-id itself is
too!

List-Id: 
=?utf-8?B?IkZvcnVtIFDDqWRhZ29naXF1ZSIgPG1vb2RsZWZvcnVtMjUvbW9vZGxlQG0=?= 
=?utf-8?B?b29kbGV1Ym8udW5pdi1icmVzdC5mcj4=?=

And what I normally read is:

List-Id: "Forum Pédagogique" <moodleforum25/address@hidden>

So the thing between angle-brackets is readable in normal message-mode
but not by :…

How to make that readable? why doesn’t nnmail-split-fancy acts on a
decoded buffer? I need this to correctly receive and track that mail :/

PS: I maybe posted this also on address@hidden, I was unsure of which 
mailing-list
was was appropriated, now I think I realized I was unsubscribed from it
and there are no online archive I guess…