What privacy measures are there with Email Sharing?

By default, all messages in your mailbox are shared with everyone who has the 'View' permission enabled for the Email Sharing app.

Messages with the word 'confidential' in the subject can only be viewed by the owner of the mailbox they're in until they're tagged to and shared with a Project.

Once a message is tagged to a project, only people with access to the project can read the message.