wip: add module.nix

Signed-off-by: Florian Brandes <florian.brandes@posteo.de>

config.example

@@ -14,7 +14,6 @@ sender = foo@example.com
 # start_tls = false
 # smime_cert = /path/to/cert
 # smime_cert_private = /path/to/cert.key
-# smime_to_cert = /path/to/recipient_cert
 
 [emails]
 # If you want to encrypt outgoing email, add the recipient certificate to the email