Microsoft on Thursday announced Hotmail users could block HTML images from appearing in e-mail messages, in a move meant to foil spammers trolling for valid e-mail addresses

Beginning this week, Hotmail users can choose to block HTML images from appearing in e-mail messages from senders not in their contact lists. E-mail users can open the images in unknown messages after seeing the other contents of the message. The technology targets a common technique used by spammers of inserting "Web beacons" in e-mail messages that verify an e-mail address is valid when a message is opened. "Spam is no longer just an inconvenience for consumers and the online industry," said Lisa Gurry, MSN's group product manager. "It has become a major problem, one that makes it hard for people to sort through their personal e-mail and reduces productivity." The move to block Web beacons by blocking HTML images worries some e-mail marketers who believe the moves hinder the effectiveness of HTML messages, which boast response rates nearly double that of text messages, according to DoubleClick. Yahoo! rolled out the option for its users earlier this year. Microsoft has already taken steps against Web beacons. The beta version of Outlook 11, its hugely popular e-mail client, includes the ability to block HTML graphics from the preview pane.