When “Messages Log Privacy” is enabled, all message content will be hidden (masked with *).

On “Messages Log” and “Campaigns” (“Reports”) sections:

The same goes for the API endpoints that return message content.

This setting can be enabled from UI under Settings / Security section:

When user has "Normal" as Message Log Privacy and wants to enable it, they must select "Secure" - they will have to specify a new password (two password inputs - one is to confirm).

Then, when they want to go back to "Normal" (to remove enabled "Messages Log Privacy" setting), they have to enter that password (also two text input boxes: 1-enter, 2-confirm).

In /manager area on "user settings" page, if a user has enabled "Messages Log Privacy" setting and you have  "remove_message_log_privacy_setting" permission – then you can completely disable/remove the "Messages Log Privacy" (and user will go back to "Normal"):

This can be useful in cases where the user has enabled “Messages Log Privacy” and wants to disable it, but cannot do it because he forgot the password.