NEW YORK - Sometimes the only way to know whether an e-mail got through is to call.
Just ask Ashley Friedlein, who runs E-consultancy Ltd. in London. He never heard back from a correspondent in the United States, a subscriber of Verizon Online. So he phoned and learned his e-mail was never received.
"I wouldn't have known anything about it had I not called to check" he said.
Blame the mishap on increasingly aggressive spam controls employed by Verizon and other e-mail operators.
As spammers identify new tricks for sneaking their junk past software sentinels, service providers' technical parries could put even more legitimate mail at risk.
Spam and spam-fighting have "in some cases eroded the reliability of the mail system," said Eric Allman, chief technology officer of leading e-mail software vendor Sendmail Inc. "Now a lot of mail gets filtered out."
A typical user might lose anywhere from a legitimate message every few months to as many as five a week, estimates Richi Jennings of Ferris Research.
A lot of spam simply ends up in junk folders that recipients never check. But sometimes service providers reject such messages outright, meaning recipients have no control even if they turn spam filters off. In such cases, senders don't always get non-delivery error messages, even though Internet standards encourage them.
Most of the recent complaints have been directed at Verizon.
Though the company denies it has changed its policies, leaked excerpts from an internal memo that circulated late last year talked of new techniques that might disrupt legitimate e-mail.
Verizon spokeswoman Bobbi Henson confirmed the memo's existence but said it contained inaccuracies and had been retracted.
Henson denied assertions that Verizon had blocked entire countries in Europe based on their Internet addresses, and she said decisions to block certain service providers were limited to a few in Asia that were sending nothing but spam. She insisted Verizon's anti-spam controls were standard industry practices.
Still, complaints continue.
Joseph Gaila, a Lithuanian now retired in Ellicott City, Md., says he and his wife missed several Christmas greetings from relatives abroad. He said he used to get one or two messages a day from Lithuania but suddenly received none for weeks.
Fabio Turone, a science journalist in Milan, Italy, says he tried unsuccessfully from at least three different accounts to e-mail a Verizon customer in Kingston, N.Y. Finally the pair created a Yahoo message group to communicate.
Five Verizon customers have jointly filed a lawsuit in Los Angeles Superior Court, alleging Verizon breached its contract by failing to provide a dependable e-mail service. A Philadelphia-area law firm is seeking arbitration, arguing that it lost potential clients.
"When you go to work every day, you expect e-mails to you will be gotten to you on a regular basis," said Michael Boni, a Philadelphia attorney who filed both cases.
Henson, who had no comment on the litigation, acknowledged that legitimate mail could get lost or delayed, but said customers were demanding action, because as much as 80 percent to 90 percent of all incoming e-mail is now junk.
"If we didn't block we would have so much volume that our platform couldn't even handle that," she said. "Instead of just a small number of customers not (getting legitimate mail), virtually everyone would not be getting mail."
Verizon offers a completely unfiltered e-mail account upon request but few have opted for it, Henson said.
Although Verizon has been getting the recent attention, it is hardly alone in misclassifying legitimate messages as spam.
In the industry, such mail are known as "false positives." E-mail lists and newsletters sent in bulk are often misclassified.
There's no good way to tell which service providers are better at handling legitimate messages because they all tend to be secretive about their specific techniques and change them regularly to keep spammers off guard.
Nonetheless, some service providers are becoming more aware of the risks.
"On a percentage basis, generally it's not a huge issue," said Kevin Doerr, product unit manager for Microsoft Corp.'s Hotmail service. "Of course, for most human beings, one false positive is one too many."
In response, Microsoft and Yahoo Inc. say they now have mechanisms for quickly refining filters should users start reporting mail in spam folders as "not junk."
E-mail providers are more willing to let legitimate senders prove their worth and get themselves on "always accept" white lists, said Stephen Currie, director of e-mail products at EarthLink Inc.
"Before, it was all, 'Let's identify the bad,'" he said.
Microsoft, Yahoo and America Online Inc. also have been working on ways to authenticate e-mail senders - to identify legitimate senders and bless their messages before spam filters kick in.
But even as service providers get smarter, so have spammers.
They have new software that automatically routes junk messages through a real user's Internet service provider so spam traffic gets mixed with legitimate mail.
"We're going to start seeing more stories of desperate ISPs blocking all mail from Comcast, Verizon, Cox and Road Runner," warned John Levine, co-author of "Fighting Spam for Dummies."
Bruce Gingery, a security consultant in Cheyenne, Wyo., says users should simply get used to losing mail.
"Even though people are relying more and more on e-mail, e-mail was never designed as a guaranteed delivery medium," Gingery said.
Service providers, he said, are only required to make a "best effort" - a term left open to wide interpretation among mail providers.