In accordance with an example implementation of this disclosure, an email handler comprises email processing circuitry, a web server, and a database. The email processing circuitry is operable to generate a uniform resource locator for a notification object to be embedded in an email message. The email processing circuitry is operable to embed the notification object in the email message. The email processing circuity is operable to send the email message into a network. The web server is operable to receive a request sent to the uniform resource locator by a client device, The web server is operable to determine characteristics of the client device based on content of the request. The web server is operable to store the characteristics in the database. The web server is operable to control access to content by the client device based on characteristics of the client device stored in the database.