Re: Signing a message with S/MIME in Gnus?

[Jens Lechtenboerger]

On 2022-11-02, at 20:51, Angel de Vicente wrote:

> [...]
> But here is a question. To send messages to this group I use another
> e-mail address (which is not present in any of the certificates). There
> is no way for me, then, to sign messages to this group with S-MIME?

There is.  Before coming to that, please reconsider for what you
ask: Alice sends a message to Bob, but the message is signed by
Mallory.  What is Bob supposed to do with this?

IMO, the signature should really match the sender’s FROM address.
Maybe you can ask your CA to include your other e-mail addresses as
well?  Or switch to GnuPG for your other e-mail addresses, where you
are in control and not some CA (which Bob probably does neither know
nor trust anyways)?  See [1] for more information.

Coming back to your question: You can customize
mml-secure-smime-signers to include a list of IDs of signing keys.

Best wishes
Jens

P.S. Google “protects” you from receiving my e-mails addressed to
you directly as I spoof my FROM address here (SPF and DKIM both
550-5.7.26 do not pass).  Thus, I remove your e-mail address in this
reply.

P.P.S. If you do not need direct replies, Gnus (Message, in fact)
can set a Mail-Followup-To header [2].

[1] https://blogs.fsfe.org/jens.lechtenboerger/2013/12/23/openpgp-and-smime/
[2] 
https://www.gnu.org/software/emacs/manual/html_mono/message.html#Composing-a-correct-MFT-header-automagically