Outlook is now the most popular e-mail tool in the world, used by hundreds of millions of people. And Smith, 23, thinks that the program is so poorly suited for most people’s intensive e-mail habits that he has a co-founded a company, Xobni, intended to fix it.

"Using Outlook today is like taking a Volkswagen Beetle into space," Smith said. "People are kind of exerting all these stresses upon it that it wasn’t originally designed to withstand."

Xobni, based in San Francisco, is introducing a new tool on Monday that plugs into Outlook. Smith’s general complaint -- one that is shared by many users of Outlook -- is that the more the program is used, the slower it gets and the harder it is to search for e-mail addresses and phone numbers.

To solve these problems, Xobni ("inbox" spelled backwards and pronounced zob-nee) has produced free downloadable software that, once installed, indexes all the e-mail in Outlook and makes those messages quickly and easily searchable. The software, available at www.xobni.com, will also be sold to companies.

Other programs, like Google Desktop, perform that same basic index-and-search function. But Xobni, which its creators call an "intelligent filter," adds a few more features.

When it scours the inbox, it extracts phone numbers it thinks are associated with the sender. So when a user searches for a person, Xobni presents the number in a side panel to Outlook.

The software also interprets the social relationships between people who are sending messages to each other. For example Xobni recognizes that if an executive sends a copy to someone else on each message he or she sends, it might be to an assistant or another colleague.