A method and system of filtering incoming email messages is provided which, on receipt of an incoming email, issues an email challenge to the sender of the received email requesting that they in turn send an email confirmation confirming that they are the sender of the originally received email, and in which received emails are then processed further according to whether or not they are occupied by a corresponding confirmation email. Senders that provide the requested email confirmation can be added to an approved list of senders such that subsequent emails received from them are not challenged again, whilst those emails to which an email confirmation is not received in response to the issued challenge can be deleted from the user's email system and the sender added to a blocked list of senders such that subsequent emails from a blocked sender are automatically ignored.