Billionaire entrepreneur Mark Cuban was an e-mail zealot at a time when most people couldn't locate the @ symbol on their keyboards. In the quarter of a century that he has been launching, buying, and selling companies, Cuban has handled virtually every aspect of day-to-day management using e-mail, starting with CompuServe and early local network-based programs back in the 1980s. He argues that e-mail is hands down the most effective way to get anything done. That includes interacting with the press: Cuban used his favorite medium to respond to Inc.'s questions about his favorite medium.

How much work-related e-mail do you receive and respond to every day?

It just depends on what is going on. 500 or more received. 100 or more responded to.

Do you have a regimen? Doing e-mails at certain times during the day or things like that?

It's continuous. Whenever I have a break, I'm checking e-mail on my phone, laptop, or PC. It keeps me in touch and is much more effective than talking on the phone. I can do e-mail on my schedule. Plus, it gives me documentation. I can do a Google e-mail search going back to 1995.

What's your criteria for what you respond to and what you don't?

If it's of value, I respond. If not, not. Some people write a book. I don't get past the first paragraph. Other people start out with some explanation of why they are writing. I don't get past that. If you are clear and to the point and it's relevant to something I am doing or am interested in, there is a good chance I will respond.

Do you use filters? If so, what kinds?

Yes. If I do business with you on an ongoing basis or you work for one of my companies, you get to the top of the list.

Are you a keep-my-inbox-pruned-down-to-one-page kind of guy or a keep-everything-so-I-have-a-record-of-it kind of guy?

I definitely don't keep everything. Not even close. I save probably only 10 percent or so of the e-mails I get. But over time, that adds up to a lot. I keep what I think might have value as a reference. In the morning, I start with just unread e-mail and work through that. It also allows me to use e-mail as a tickler file. If I need to revisit something, I will mark the e-mail as unread. Then the next time I go through my e-mails, it's right there. So it keeps things manageable.

How much time do you estimate you save by running so much of the business via e-mail? And what are the biggest time savings?

Five to 10 hours per day. No meetings. No phone calls. Everything is documented so the number of "let's talk again" or "get together to clarify" or "get on the same page" are gone. People learn very quickly to document and get to the point without the "intonation" of trying to sell me that occurs in meetings. I'm a Dragnet type of e-mail guy. Nothing but the facts. Leave the BS for other people.

Has e-mail mastery taught you anything about more efficiently and effectively conducting face-to-face communications?

It has really taught those around me. If you are going to ask me to be in a meeting, there had better be a lot of business closed and delivered, or we are going to have issues.

Any cool e-mail tricks that more people should be aware of?

Learn how to use the filters and labels so you can quickly get to information. Also, I often keep two instances of my e-mail accounts open so I can search on one while reading and responding in the other.

The biggest gripe I hear about e-mail is it's rarely just a simple exchange. Response begets response begets response. In person or on the phone, by contrast, the parties reach agreement, and that's all she wrote. What say you to that argument?

I couldn't think of a bigger lie. Why would the back-and-forth be any more in e-mail versus the phone? Anything you can say on the phone, you can put in an e-mail. Any deal of consequence you close on the phone is going to have to be documented. Someone is wasting a boatload of time trying to transcribe what two people thought they said and heard.

Do problems arise when you have a critical business relationship and the CEO of one company is a committed e-mail person, and the CEO of the other company is a committed phone or face-to-face person?

The person who is spending the money makes the decision. As in any business situation, money talks. If the deal is big enough, you can call me anytime.