email: Open firewall port for managesieve protocol

- managesieve plugin is already enabled due to installation of
dovecot-managesieve.

- Using ManageSieve protocol, clients like Thunderbird (with managesieve addon)
will be able to edit mail filters on the server. The server will perform the
filtering enabling all clients to share the benefits.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

plinth/modules/email/__init__.py

@@ -105,7 +105,9 @@ class EmailApp(plinth.app.App):
                         listen_ports=[(6379, 'tcp4'), (6379, 'tcp6')])
         self.add(daemon)
 
-        port_names = ['smtp', 'smtps', 'smtp-submission', 'imaps', 'pop3s']
+        port_names = [
+            'smtp', 'smtps', 'smtp-submission', 'imaps', 'pop3s', 'managesieve'
+        ]
         firewall = Firewall('firewall-email', info.name, ports=port_names,
                             is_external=True)
         self.add(firewall)