NEW YORK (AP) -- As an online newsletter publisher, David Carney has discovered one thing about e-mail delivery: You can't always count on it.
On average last year, about a dozen copies of Carney's "Tech Law Journal" wouldn't get through each day, mostly thanks to overzealous e-mail filters set up to block junk mail, pornography and computer viruses.
To reduce blockage, Carney has misspelled "pornography" and "sex" when writing about adult content issues. He has also dropped links and paragraphs that contain ".exe," characters sometimes mistaken for a virus.
Though the glitches affected less than 1 percent of his subscribers last year, they were enough to be annoying.
They also offer a cautionary tale to Internet users who increasingly depend on e-mail for important tasks like paying bills and trading stocks.
"E-mail is not a method of delivery that's certain of reaching the recipient," Carney said.
Like other Internet traffic, e-mail typically passes through three or four different networks to reach a recipient. Each network pledges to make its best effort at passing data along, but that's not a guarantee.
Though e-mail will often find another route when an intermediary network breaks down, messages are occasionally lost in transit.
At times, messages can even get routed to the wrong e-mail box.
In addition, recipients and their mail providers sometimes install filters to block unwanted e-mail, inadvertently delaying or deleting legitimate messages that contain certain words or characteristics.
Internet service providers also can go out of business, making entire e-mail accounts inaccessible. Recently, about a million Excite(at)Home users lost e-mail abruptly. Others are to lose accounts over the next month.
With e-mail, senders sometimes get an error message when something goes wrong. But that's not guaranteed.
"The network is not infallible, and it's not designed to be infallible," said Bill Robertson, a senior vice president at NETdelivery Corp. in Boulder, Colo.
Robertson said e-mail is fine for casual uses, but basic e-mail systems won't do for critical business functions involving contracts and bills. NETdelivery and other companies now offer receipts and other supplementary services, similar to certified and registered "snail" mail.
Online billing company Princeton eCom is developing a system that ensures important notices get through, while competitor Paytrust will send reminders if a bill remains unpaid as a due date approaches.
At Datek, an online brokerage, nearly three-quarters of stock confirmations are sent electronically, at the customers' request.
Because glitches occur, backup systems are in place, said Michael Dunn, a Datek spokesman. If e-mail repeatedly fails, he said, "we will automatically generate paper and send it out by mail."
Harvard University recently got a firsthand lesson in reliability.
Demonstrating the importance Internet users place on e-mail, 93 percent of applicants through Harvard's early action program asked to be notified by e-mail in addition to regular mail.
But of 6,000 decisions sent out, about 100 were returned, even after excluding AtHome addresses.
Marlyn McGrath Lewis, Harvard's admissions director, said mailboxes may have been full or had filtering in place, and anxious applicants ended up calling the admissions office. She said Harvard has no plans to drop postal mailings.
Not that snail mail is problem-free, either. Letters sometimes get stuck in sorting machines or misdelivered to a neighbor. During the anthrax scare, several items -- including college placement exams -- sat undelivered for weeks.
In fact, because the Internet was designed to withstand local disruptions, e-mail was the best communications medium on Sept. 11 when New Yorkers wanted to let friends and relatives know they were OK. Telephones were jammed; postal mail was too slow.
But Internet users, particularly newcomers, may be too trusting of e-mail.
"They think it's like the postal office," said Laura Gurak, director of the Internet Studies Center at the University of Minnesota. "They don't realize these messages bounce all over the place."
Michael Weir of PostX Corp., a company that offers receipts and other supplemental e-mail services, estimates that 97 percent of e-mail gets through the first time.
Most of the remainder, he said, are automatically resent and get through. Only rarely would a message get lost or bounce back.
Michelle Pavolka, a systems engineer at Premera Blue Cross in Mountlake Terrace, Wash., considers mishaps an inevitable side effect of combatting junk mail and viruses.
She uses Baltimore Technologies' MIMEsweeper software to catch thousands of unwanted messages a day, accidentally filtering out only a dozen or two legitimate messages.
Most of those errors, she said, are caught by day's end in manual reviews.
Even if a message gets through, though, there's no guarantee it will actually get read.
"If I knew it was important ... I would probably call you" as well, said Bruce Schneier, chief technical officer at Counterpane Internet Security.
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