Sheryl Patton runs a lean operation. She started her catering business, Make Me Lunch, in San Rafael, Calif., last November -- and she still doesn't have a business telephone number. "I rely on faxes and mostly on E-mail," she says. Not just any E-mail. Patton uses free, Web-based E-mail (in this case, Microsoft's Hotmail).

Free E-mail. This Internet marketing strategy sounds like such a bargain. Popular Web portals and news and entertainment sites offer the service -- you'll find variations at Yahoo!, Excite, and even Business Week Online. For access to your account, just visit the Web site via your browser and log on.

No question the services are popular. Hotmail claims to be the market leader with 40 million active users. It's also clear why sites offer this giveaway: It brings repeat visitors, making the sites attractive to advertisers.

But why would a business person such as Patton use free Web-based E-mail? If you have an Internet service provider, you get an E-mail account at no extra charge. For access to an ISP mail account, you use widely available E-mail software such as Qualcomm's Eudora, Microsoft Outlook Express, or Netscape Messenger. The latter two are part of those companies' browsers, which can be had for free from their Web sites and elsewhere. These programs download messages from your ISP mailbox onto your hard drive, so you can call up messages almost as soon as they come in. On the other hand, getting messages via a site-based free E-mail account takes as long as loading a Web page. And the process is hostage to all the same technical bottlenecks you can run into while surfing the Web.

NO DOMAIN NAMES. Another disadvantage of promotional, Web-based E-mail is you can't use your business' registered domain name -- if you have one -- in your address. A typical business E-mail address is myname@acmewidgets.com, a format that's easy to remember. For an additional fee, ISPs will let you use an address such as that -- instead of their name after the @ symbol. With a Web-based E-mail, you're stuck with the service's name. Patton's E-mail address, for instance, is makemelunch@hotmail.com.

Still, there are two real advantages to free Web E-mail services: They're accessible when you're out of the office from any computer with a Web connection. And you can use them to get mail from other, less-accessible accounts. "I can check my E-mail from the public library, from a customer site, from wherever I am," Patton says. To get her ISP E-mail account, she first must connect to the provider. But that's not always possible. Clients may use other ISPs, for example. And few businesspeople want to inconvenience customers with requests to hook up a laptop to a modem.

You can tap other mail accounts via the Web-based services simply by logging on and following instructions to get external mail. But only some ISPs will let you do so.

Which Web-based E-mail service is best? We looked at Yahoo! Mail (www.yahoo.com), Hotmail (www.hotmail.com), and BusinessWeek Mail (www.businessweekmail.com) and found they have similar features, including the ability to create folders in which you store messages and to maintain an address book of your E-mail recipients. They all have so-called filters that examine incoming messages for certain elements, such as whether a message comes from a key client. The filters automatically route messages to specific folders. Filters are easy to set up using on-screen forms in your browser, which you access from the home page of the service.

Because these E-mail offerings are so similar, you may want to select one on the basis of which is most pleasing to your eye. We found Hotmail the easiest to navigate. Or, if you regularly visit one of the popular portal sites, such as Yahoo!, Excite, NetCenter, or InfoSeek, you might as well use that service's E-mail.

Patton says when she started her business, she didn't have an account with an ISP. She does now. Still, Patton won't change her free E-mail address: "This system has worked out really well. Everybody knows my E-mail address."

David Haskin in Madison, Wis.