Yes, go to consumers, policy, select default policy (in which new external users belong as default), Edit Web Messenger settings.
These are delivery options to choose:
Delivery Options
The selected delivery types will be available to external users on the Web Messenger Options screen.
PGP Universal Web Messenger
Provide users with the option to save sent messages on the server
Enable the "save sent messages" option by default
PGP Universal Satellite
PGP Desktop or S/MIME
PDF Messenger
Regular Email
You can change behaviour if you create a new rule in the email policy chain "inbound"