add a configurable list of recipients/cert dict

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

config.example

@@ -8,10 +8,16 @@ port = 465
 username = foo@example.com
 password = s3cr3t
 sender = foo@example.com
-recipients = monitoring.foo@example.com, John Foobar <foo@baz.org>
 # set_reply_to = false
 # use_tls = true
 # start_tls = false
 # smime_cert = /path/to/cert
 # smime_cert_private = /path/to/cert.key
-# smime_to_cert = /path/to/recipient_cert
+# smime_to_cert = /path/to/recipient_cert
+
+[emails]
+# If you want to encrypt outgoing email, add the recipient certificate to the email
+# if not, add an empty string
+# uses email = Path to certificate
+# monitoring.foo@example.com = /path/to/recipient_cert
+# unencrypted@example.com = ""