end-to-end encryption

[guggi2000]

There is a big discussion about end-to-end encryption, for example on Facebook Messenger, WhatsApp... especially for mobile phones.

Would you say that a "messenger.com" message from a web browser running under "https" would be encrypted and non-readable between the PC and the Facebook servers?

[phranque]

you can only be sure it is encrypted between the securely connected endpoints.
you cannot be assured of encryption between facebook servers.

for example:
Yahoo, Google still working on end-to-end encryption for email [sfchronicle.com]
(from 2017)