(FORTUNE Magazine) – Since the introduction of the PC in the early 1980s, people have searched for "killer apps"--the software that leads to hardware sales. The first one was the spreadsheet. Then, when the Internet emerged, people looked for its killer app. Maybe it's the Web browser, some said. Now it has become clear that the real killer app is e-mail. Sometimes it feels as though e-mail is trying to do just that: kill us.

I've been dealing with the problem of being choked by e-mail for a long time. Recently I've seen how the issue looks when multiplied across an entire corporation. Over the past few months my partners and I have studied startups that help manage storage issues for large companies. Here's an amazing stat from that exercise: Nearly half of large companies' storage space is now occupied by e-mail. The exact number is hard to nail down, but that feels right. We are all using e-mail so much that our messages and the documents attached to them--PowerPoint slides, Excel files, Acrobat documents, not to mention random photos and audio files--are beginning to outpace the demands for space from companies' databases of customers, inventory, and accounting information.

While the crush of e-mail taking up our nation's disk space is a problem, I'm more worried about how it's taking over my life. At Demo 2003, a conference I just attended in Scottsdale at which geeks mostly show their wares to other geeks, a presenter said that the average worker now spends more than two hours a day reading, responding to, or disposing of e-mail. It's true of me. I sometimes wonder whether I am really being effective in my job spending half the time in e-mail, half the time on the phone, and the other half doing real work.

It's no surprise that entrepreneurs have seen that there's money to be made in taming this e-mail mess. The most innovative products I saw at Demo were programs designed to keep e-mail away from me, organize it, or make the information it contains accessible to colleagues who need it.

Let's take the first one first. The problem of spam is well understood: It's so cheap to send millions of solicitations by e-mail that it's worth doing even if virtually no one responds. On average, a spammer needs response rates of only 0.1% to make sending worthwhile. Now programmers are beginning to figure out how to identify spam pretty accurately and remove it automatically from your in-box. Even better, they're building "spam walls" that kill messages before they even get to your in-box. My favorite spamware is made by (no surprise) one of my portfolio companies, MailFrontier, in Palo Alto. Since I installed it last fall on my PC (a server version was unveiled at Demo), it has identified and removed 3,985 messages from the 17,406 I've received.

Fortunately (I think), most of my incoming e-mails are legitimate. That brings me to the problem of organizing. I used to pride myself on reading and responding to every e-mail. I got over that, but now I worry that I'm failing to read the messages I should, or failing to route them properly to partners and colleagues. Currently, for instance, I have 175 items in my in-box, all of which I've read. But I don't always know what to do with them right away, so I move to another message before taking action. When I get really busy, I'll have as many as 500 items in my in-box, with as many as half unread. I just have to wait until I have the time--usually on coast-to-coast flights--to read the unread ones and process the others.

A little company called Open Field Software in Santa Cruz, Calif., introduced a plug-in for Microsoft Outlook that automatically classifies and sorts e-mail based on your preferences. I'm suspicious of anything that promises to learn what you want, but this software, which uses complex heuristics to match similar e-mails, was persuasive. Since it could move maybe half of my e-mails automatically to a different folder for later reading, what would remain (after deleting spam) might be manageable in a day's work.

So there are programs to get my e-mail whittled down and organized, but what about putting it to use? Another thing I learned while researching companies' storage space is that my colleagues' e-mail actually contains most of what I want to know. I don't really care about their back-and-forths. The really juicy useful stuff might be a number in a PowerPoint presentation or a key fact in a Word document, each of which was stored as an attachment to an e-mail sent two months ago.

Kubi Software of Lincoln, Mass., introduced an add-on to Outlook and Lotus Notes that enables users to store e-mails and all their attachments in one area--and then lets the information be shared with as many workers as necessary. The coolest part is that Kubi lets you quickly find the content of the attachments to other people's e-mails.

The thing I'm most leery of is how these companies (including the one I invested in) plan to thrive. Each product is based on working with Outlook. Makes sense; 70% of office workers in large companies use the program. But it's also unstable and undependable, making it hard to maintain add-ons. And there's nothing to keep Microsoft from just integrating the best parts of these add-ons into future versions of Outlook.

But even if Microsoft turns out to be rapacious (is there a doubt?), even if it's hard to get customers to pay much for e-mail add-ons--heck, even if the companies aren't all that successful--I still came away from Demo thinking that maybe the future will mean we'll finally get control over the killer app for the Internet. And that it won't kill us to read our e-mail anymore.