I just used git-send-email the first time since ages. When it finished, I saw a stream of 16 warnings:
Warning: unable to close filehandle properly: Bad file descriptor during global destruction.
The invocation was this:
git send-email --to git@vger.kernel.org patches
where the argument 'patches' is a directory with 4 patches.
The patches were sent quite fine, as it seems. I can help debug if someone is interested.
-- Hannes