On Wed, Apr 11 2012, Olivier Berger <olivier.berger@it-sudparis.eu> wrote:
> Is there a way to decrypt multipart/encrypted messages in notmuch-emacs

Hi, Olivier.  Yes, it is possible.

> I can only get a purple "Decryption error" message...

The fact that you're getting this messages means that notmuch is
attempting to decrypt the message, but there was a decryption problem.

A typical problem is that gpg-agent is not running.  Notmuch uses gnupg
to decrypt, but it requires that gpg-agent be running to get the
passphrase from the user.  Do you have gpg-agent running?

> The mail looks like :

The format of the multipart/encrypted looks fine, so I see no problems
there (assuming the encryption was done properly).

You might also try decrypting the message on the command line, as that
will take any emacs issues out of the loop:

notmuch show --decrypt id:$msgid

It might help to redirect stdout to /dev/null to make it easier to see
any gnupg error messages

I hope that helps.  Let us know if you still can't figure it out, or if
you have other questions.

jamie.