A method for securing messages includes obtaining, at a message server, a message for a user of a message service hosted by the message server. The message includes a header and the header includes a digital signature signed by an author of the message and a list of one or more recipients of the message. The method includes determining whether the digital signature by the author is valid and determining, using the list of one or more recipients, whether the user is a declared recipient of the message. When the digital signature by the author is valid and the user is the declared recipient of the message, the method includes delivering the message to a user device of the user. When the digital signature by the author is valid and the user is not the declared recipient of the message, the method includes alerting the user.