In the year 2009, on the 25th of April, a man named Greg is supposed to get an e-mail. It will remind him that he is his own best friend and worst enemy, that he once dated a woman named Michelle, and that he planned to major in computer science.

"More importantly," the e-mail says, "are you wearing women's clothing?"

The e-mail was sent by Greg himself — through a Web site called FutureMe.org. It is one of the messages open to public view at the site, and Greg used only his first name.

FutureMe is one of a handful of Web sites that let people send e-mails to themselves and others for delivery years in the future. They are technology's answer to time capsules, trading on people's sense of curiosity, accountability and nostalgia.

"Messages into the future is something that people have always sought to do," said Paul Saffo, director of the Institute for the Future, a research group. "In a way, it's a statement of optimism."

Matt Sly came up with the concept for FutureMe.org about four years ago after recalling how, during his education, he had been given assignments to write letters to himself.

Sly, 29, who partnered with 31-year-old Jay Patrikios of San Francisco on the project, said the site has made maybe $58 through donations. He insists it is not a reminder service and that users should think in the long term.

FutureMe and other service providers try to make the delivery process fail-safe through partnerships or back up software, and they urge people to hang on to their e-mail address, but there's no ironclad guarantee that the message will ever arrive.

FutureMe lets people send messages for delivery as much as 30 years from now, though Sly's numbers show most users schedule their e-mails to be sent within three years.

"We want people to think about their future and what their goals and dreams and hopes and fears are," he said. "We're trying to facilitate some serious existential pondering."

He said a large number of the messages do one of two basic things: tell the future person what the past person was doing at the time, and ask the future person if he or she had met the aspirations of the past person.

"The tone of the past person is not always friendly," said Sly, now a Yale University graduate student. "It's often like 'Get off your lazy butt."'

Recently, Forbes.com jumped on the idea, offering an "e-mail time capsule" promotion. More than 140,000 letters were collected over about six weeks. Nearly 20 percent are supposed to land in the sender's inbox in 20 years but others requested shorter time frames. Forbes.com is partnering with Yahoo! and Codefix Consulting on the project.

"A lot of people have kind of been freaked out by it," said David Ewalt, a Forbes.com writer who worked on the project. "It really makes you stop and think about your life in a way that you usually don't."

Another type of future message service can be found at sites such as myLastEmail.com or LastWishes.com, which promise to send messages to loved ones (or less-than-loved ones) after the writer's death.

Paul Hudson, co-founder of the International Time Capsule Society, said e-mail time capsules were new to him.

"Part of the value of time capsules are that they are thought processes in the present," said Hudson, a historian who teaches at Georgia Perimeter College. "You define yourself when you do a time capsule. It might be a good exercise in introspection."

But sometimes the past is best left behind, said Saffo, who personally finds the whole thing "sad and really weird."

"The lesson about all these things, it's the lesson from time capsules, is you have to be careful lest you set yourself up for enormous embarrassment in two decades," Saffo said. "Do you really want to be reminded that you thought ABBA was cool?"