Thus, a mechanism must be setup to allow users to manage their content on other sites. The mechanism that I currently planed was to use email verification (if (User's email === poster's email): They're the owner of the post), which requires all sync sites knows the email address (as an universal identifier) of the content owner.
To me, that means I need to share user's email with other sync parties which may not under my control. Because of that, I think it's sanctimonious to tell user that their email is under protection, I rather letting user be very aware about their email will be publicly displayed.
Another reason to publicly display users email is because I don't want to implement private message features (Which require to save private information), so if user's can know each other's email, they could just make content with their emails.