I have asked our employees to login to RingCentral via web browser and send their faxes online to ensure the faxes are not sent over the Internet unencrypted.
According to an old conversation, fax-to-email that is sent FROM RingCentral is sent via TLS, when available.
We have opportunistic TLS enabled on our mail servers. I can make some assumptions here, but I need it to be explicitly stated, and can't find it anywhere: Can RingCentral accept TLS-encrypted email-to-fax (via ##########@rcfax.com)?