(FORTUNE Magazine) – Years ago, to support my computer habit I started hawking software by mail. When people actually began ordering, I naively bought sheets of stamps in various denominations, but they never quite matched up with the weight of the packages I mailed. I rented a postage meter, which was more flexible. But it was also more costly, and it seemed to run out at inconvenient moments, resulting in hurried trips to the post office.

In short, mailing stuff is a pain. So I was intrigued when the government announced last month that it would let me buy postage over the Net--eliminating all those hassles. The new system works but has enough gotchas to make me think twice before surrendering my stamp book.

I signed up with E-stamp of San Mateo, Calif., the first PC postage vendor to win approval from the U.S. Postal Service. The company's $49 startup package, which includes a $25 postage credit, is aimed at the SOHO (small office/home office) market--people who generate more mail than the average monthly bill payer, but not enough to justify a meter.

The kit includes two CD-ROMs and a small "electronic vault," a gadget that installs between your computer's parallel port and printer. The password-protected device stores the postage you download from E-stamp's Website so that you can print stamps offline. Rival vendor Stamps.com, which goes live Sept. 27, doesn't require special hardware, but you must be online to print postage.

E-stamp's finicky software refused to run on my Dell Dimension but installed without a quibble on a generic Pentium II machine. Once it loaded, I logged on to E-stamp's Website to set up my account. Since stamps are U.S. currency, the government is fussy about who gets to print them, and you'll have to wait up to 24 hours for the Postal Service to approve your meter license. Eventually you'll be able to buy postage with a credit card, but for now the Postal Service accepts only electronic fund transfers. E-stamp offers simple instructions for setting these up.

Printing a single envelope was easy enough too: Just enter the recipient's address, select the amount of postage, and click "print." It took 20 seconds for the stamped envelope to emerge from my HP LaserJet. E-stamp can import address lists from Microsoft Outlook and other popular contact managers, allowing you to print an envelope or label just by clicking on the recipient's name. But try to get fancier, and you run into roadblocks. For example, E-stamp's software integrates with Microsoft Word for printing a single address, but you can't run off a batch of envelopes or labels using Word's popular mail-merge feature.

The Postal Service makes things worse by imposing conditions that make its life easier and yours harder. For starters, to print postage you must have an address-matching CD in your drive, which E-stamp uses to produce a zip-plus-four-plus-two bar code. Worse, you have to print an address at the same time you print a stamp. So you can't print postage on a pre-addressed envelope or run off a bunch of labels.

Then there's the cost issue. E-stamp adds a 10% "convenience fee" to your purchases, with a minimum fee of $4.95 and a maximum of $24.95 per download. So it pays to buy at least $50 worth at a time. You have to weigh those costs against renting a meter, which can run as little as $20 a month. If you mail a mix of letters and small packages every week, PC postage may be worth it. But if you're a heavy user with regular mass mailings, stick to a meter.

For information on E-stamp, call 800-4estamp or surf to www.estamp.com. For a list of other PC postage vendors, check out the Postal Service Website at http://ibip.tteam. com/html/pcpostage.html.