New issue by Eluminae on mblaze repository

https://github.com/leahneukirchen/mblaze/issues/202

Description:
I just configured filters with some contrib scripts from this repo and I received this mail

```
--- 1: multipart/encrypted size=2246 filter="mgpg" ---
--- --- 2: multipart/signed size=1138 ---
--- --- --- 3: text/plain size=356 ---
This is a test email sent from sourcehut to confirm that PGP is working as you
expect. This email is signed with this key:

447B 69E4 B34B E90B C829 A0E9 6597 04D1 A38A 93AE

and is encrypted with this key:

CAB1 2F60 BD13 A21D AB60  C510 5BAC 9232 8B7C 5D65

You may control your PGP settings here:

https://meta.sr.ht/privacy

--
Drew DeVault
sourcehut
--- --- --- 4: application/pgp-signature size=455 name="signature.asc" render="mverify; exit 0" ---
No signature found.
```

It seems this signature could not be verified.

After some check, it seems I can't send an encrypted + signed email too

In recap:

* Is it possible to encrypt then sign ? Or to encrypt+sign in one action (maybe easier) ?
* Does mverify and/or mpgp could handle signed crypted messages ?