An altruistic Google employee has come up with a system that will block — or at least make people reconsider sending — the type of message they will probably regret the next day. Mail Goggles, which can be set to spring into action late at night and at weekends, asks emailers to answer a series of short maths questions before sending a message. The basic addition and multiplication sums have to be completed within a time limit. The idea, according to the Gmail engineer Jon Perlow, is to help those who are a little too tired and emotional to foresee the consequences of their actions. "Sometimes I send messages I shouldn't send," Perlow confessed on the Gmail blog. "Like the time I told that girl I had a crush on her over text message. Or the time I sent that late-night email to my ex-girlfriend that we should get back together."