(FORTUNE Magazine) – In case you haven't heard the term before, a "killer application" is the holy grail of the computer industry. A killer app, as it's also known, is a piece of software that motivates people to engage in the unnatural act of buying computer products they wouldn't have dreamed of buying before. The original killer app was VisiCalc, the first spreadsheet program, which ran on the Apple II. It got people to buy Apple II computers when no reasonable nerd could have predicted they'd do such a thing. VisiCalc made Apple Computer a hot company back in the late 1970s.

E-mail is the killer application of the Internet. Even if you've never used a computer, you'll eventually realize that you need E-mail. You'll get the computer, stumble your way through hooking it up, acquire the Internet or network account you need, and set up an electronic mailbox.

I've been using E-mail since 1985, when I became a subscriber to MCI Mail. Some people live in their word processor; some people live in their spreadsheet program. Some even live in their presentation program or personal organizer. I live in my E-mail. I vaguely remember what it was like not having E-mail and what it was like to realize that I wanted it. My memories of the arduous process of getting it to work are not vague. They're painfully vivid. I've never met an E-mail package I actually liked. I've been complaining vigorously about these programs for years.

Now, 13 years later, things are different. It seems as if everyone's addicted to E-mail. It's nice that E-mail has gotten easier to use, but its widespread nature presents a whole new set of problems. Take this morning. In the 45 minutes that I messed around trying to avoid writing this column, I accumulated 20 new E-mail messages, wrote three outgoing ones, and read and deleted ten others. This was at 5 a.m. on a Monday, before the electrons really start wailing away.

That's a lot of mail, but it's nothing compared with the stockpile that builds over any stretch of time. Counting the messages I dealt with earlier today, I now have 305 E-mails in my in-box. Seventy-nine of them are unread. I have another 1,500 or so messages stored in various folders in my E-mail program, filed according to the major topics in my life: family, portfolio companies, scheduling, and so forth. And I've got over 3,000 messages that I've deleted from my in-box in the past three months but haven't yet permanently removed.

I've learned how to read lots of mail and still have a life. And I'm not normal, I know. But perhaps my vast experience can serve as a kind of guide for you E-mail newbies out there. There is no reason that the flow of electronic messages should get completely out of control. And so I've developed Alsop's E-mail Dictums--three rules for proper behavior when communicating by electronic mail.

Never send unwanted E-mail. Of the 79 unread messages in my in-box, 20 came because someone added me to an E-mail list without asking if I wanted to be there in the first place. You may have heard this referred to as "spamming."

I've got a message titled "Jerusalem's Temples and Jesus Ingominias Death" from one Robert J. Macdonald in Honduras. I don't know what motivated Mr. Macdonald to begin mailing me a couple of years ago. But I can assure you that I have no interest in what Mr. Macdonald has to say, even if it is about how Jesus died. Fortunately, he doesn't send me messages as frequently as all those so-called public relations firms out there (the ones who take my E-mail address at the bottom of this column as a blanket invitation to spam).

As I see it, computers make it easy to target messages to people who will be receptive. Sending unwanted mail only shows (1) that you don't understand your E-mail's targeting capabilities, and (2) that you don't understand (or care to understand) what your recipient wants to read. Which leads me to my second rule:

Remember that you are talking to another human being. Why take the time to write an E-mail if you can't be bothered to make it readable? Personally, I can deal with people's inability to use upper- or lower-case characters when they write E-mails. But blowing off paragraphs and punctuation offends me. Bear in mind that there are sound reasons why these were invented: They make things easier to read. They also make it more likely that people will understand what you say. Clarity. Wow!

Write your message as though you care whether it gets read or not. Take time to write a subject line that means something to your reader. Don't assume that your readers are waiting breathlessly to respond; give them time to think before they write back. And one other thing--sign your message. I can't tell you how many times I've gotten E-mail from someone who wants me to invest millions in his company but doesn't bother to put his name in his note.

When I get an E-mail message that is little more than a stream of consciousness, I suspect that the writer didn't have enough time to figure out what he really wanted to say, and that he's now making me take the time to do it for him. I imagine that I must be less important than he is, at least in his mind. In other words, he's already off on the wrong foot.

Learn to use the technology. If you do decide to send regularly scheduled E-mail messages to a list of people (after they've given you permission to do so!), be aware of what you're sending them. Different E-mail programs display the same message in different ways. Format your note so it will look good in any program. Make sure its subject line is immediately recognizable so that your recipient can store it without having to read it first.

If you give people the option of removing themselves from your list, you should also remind them which E-mail address you are sending to (some people have more than one). Otherwise, they may not be able to get off your list very easily. This is a particularly important rule for companies trying to provide exceptional service through E-mail. When you buy a book from Amazon.com, the E-mail messages you get are properly formatted, contain precisely the information you need, and give you several actionable options if you don't like what you read. I've seen some other services send E-mail that includes tables that don't line up. This means you have to copy the message into a word-processing application and insert tabs between the columns to be able to read it. It hardly gives you great confidence in the value of their service!

Pretty simple rules, huh? When I get it down in black and white like this, though, I begin to wonder if I haven't been complaining about the wrong thing. Maybe the E-mail programs are fine. Perhaps the problem is the people! We just need people with a better user interface! Hmm... Now, that's a thought.

STEWART ALSOP is a partner with New Enterprise Associates, a venture capital firm. Except as noted, neither he nor his partnership has a financial interest in the companies mentioned. Alsop may be reached at stewart_alsop@fortunemail.com; the column may be bookmarked at www.fortune.com/technology/alsop/