For example, researcher Joshua Goodman says the ultimate solution could be a four-pronged defense against spam called SmartProof. Here's how an experimental version of it works:

-- First, a machine-learning filter, similar to SmartScreen, snags the obvious spam and quarantines it or throws it away. The filter passes on to the user's in-box any message that is from someone on the user's "whitelist."

-- Messages suspected of being spam trigger replies to the senders, challenging them to prove they're not spammers.

-- Senders may respond to the challenge by solving some kind of a puzzle -- one that's easy for a human but hard for an automatic spam generator.

-- Alternately, senders can ensure the delivery of their messages by making credit card-based "micropayments." The payments may go to the recipient, the Internet service provider or a charity, or they can be refunded to the sender if the message turns out not to be spam.

"We thought if we could put all that together, we'd have a great long-term solution," Goodman says. "Obviously, it's a very ambitious plan, and I don't think we ever thought it would happen quickly."

Elsewhere at Microsoft, researchers are working on a prototype called MailScope that monitors e-mail routes and alerts users when significant delays are expected. If MailScope sees persistent delays between, say, Microsoft.com and Berkeley.edu, it warns users on those servers that delays are likely, much as a traffic report notifies drivers of congested routes.

In a related Microsoft project called SureMail, when a message is sent, a system posts a tamperproof notification to a table somewhere on the Internet. E-mail recipients periodically query the table and match notifications with messages received. If they find a notification for which there is no message, they know the message has been lost. Microsoft calls these "silent" losses because they so often go undetected. In controlled experiments over two months, using a variety of e-mail systems and carriers, Microsoft found that one in 140 e-mail messages disappeared without a trace. Delays averaged four minutes but lasted as long as 27 hours.

Despite the extensive research and development, some observers say technology can never completely cure e-mail's ills. Economic and regulatory tools will be needed as well, they say.

"Ultimately, I believe there will be a pay-per-message type of service that charges to ensure that e-mail is spam-free," says CIO Matthew Lynch at ShopKo Stores. E-mail carriers will charge companies a penny or two per message and will in exchange certify those messages as legitimate, he says. Lynch also predicts "stronger legislation around this topic."

A combination of technology, policy and market measures will keep e-mail among the top of all corporate applications, most users say. "E-mail will continue to be an integral form of communication," says Matthew Marks, head of integrated user services at Aetna. "The capability to quickly and easily distribute a message with an attachment -- documents, links, objects, etc. -- to a large, dispersed audience with tracking and audit cannot be matched by IM, fax or snail mail."