recoding messages to latin1+html when posting to yahoo groups?

[James Leifer]

Hello,

I'm running Ubuntu gutsy with

  Gnus v5.13

  GNU Emacs 23.0.60.1 (i486-pc-linux-gnu, GTK+ Version 2.12.0) of
  2007-12-30 on iridium

and happily editing French emails and documents in utf-8 which gnus
handles beautifully for posting and reading.

My problem is that when I distribute messages via the Yahoo groups
mailing lists, all utf-8 accented characters get garbled.  I did several
experiments with mm-content-transfer-encoding-defaults to see if base64,
8bit, or quoted-printable would be handled correctly by yahoo, with no
success.  Yahoo only handles iso-8859-1.

If I had my choice, I would dump Yahoo groups and use a less broken list
manager, but I don't have this option! 

So....

Is there any way to set a gnus hook that recodes a utf-8 email into
latin1 plus html entities when sending to any address of the form
.*@yahoogroupes.fr?  I know that the unix program recode can do this
kind of thing, but I don't understand:

- which gnus or message hook I should modify;

- how such a conversion would interact with the mime handling;

- how to apply a conversion to the Subject line.

Any help would be gratefully received.

Regards,
James Leifer