Gmail, Google's e-mail system, is offering a new feature called Mail Goggles which is intended to make users think twice before firing off a message.

E-mailers who set up the new system will be asked to solve a series of simple math questions before hitting the "send" button.

The theory, according to Gmail engineer Jon Perlow in his company blog announcing the feature, is that if users' mental faculties are sharp enough to answer the questions correctly, they'll be aware of a message's potential consequences.

"Sometimes I send messages I shouldn't send," he wrote. "Like the time I told a girl I had a crush on her by text message. Or the time I sent that late-night e-mail to my ex-girlfriend that we should get back together."

Perlow derived the name from the term "beer goggles," used to describe the distorting effect alcohol can have on people's perceptions.

Goggles only kicks in on weekend evenings, when e-mailers are presumably the most vulnerable to alcohol or depression.

Gmail users can activate the service by clicking the "Settings" link at the top of a Gmail page and then going to the "Labs" section.