A method includes: accessing a corpus of messages previously sent from a user account; correlating sequences of words, in the corpus of messages, with behavior signals; aggregating the behavior signals into a behavioral model representing combinations of behavior signals characteristic of behavior in messages sent from the user account; later, accessing a message outbound from the user account to a recipient account, the message including a document associated with a document tag; correlating sequences of words, in the message, with behavior signals; retrieving a data access policy including a threshold at which access to a document associated with the document tag is restricted; and in response to detecting a difference between the behavioral signals from the message and the behavioral model exceeding the threshold, restricting access, by the recipient account, to the document in the message.