Hi,
the documentation says:
Note – Outgoing e-mails for recipients whose S/MIME certificate or OpenPGP public key are existent on the firewall will be encrypted by default. If you want to disable encryption for these recipients, delete their S/MIME certificates or OpenPGP public keys. If certificates or public keys are unknown to the security system, e-mails will be sent unencrypted.
But email are only encrypted when sending User is available with in Internal Users List.
The Note says somethinh else. I t says every Mail is encrypted when certificates/keys are available.
Sven