A filter mechanism for unwanted e-mail messages uses a downloadable central source (1, 2) of filter rule data. User reports of received unwanted e-mail messages are relayed back to the central source of the filter data and used to automatically update that filter data. An algorithmic approach to identifying characteristics of unwanted e-mail messages may be applied based upon the preponderance of predetermined words within an e-mail message or characteristics of the addressee list. If an e-mail message is identified as suspect, but not definitely unwanted, then it may be encapsulated within a HTML document and sent to its addressee together with buttons (28) allowing the recipient to provide feedback in the form of votes as to whether or not that e-mail message is unwanted. This recipient feedback may be used to establish a new local rule.