You've got mail. But don't know it.

Got a spam filter? Maybe incidents similar to these have happened to you:

• Last June, Laura Miller had some of her incoming e-mail blocked because of a new spam filter installed by her Internet service provider. Among the e-mail filtered out: messages from The New York Times, costing Ms. Miller, senior editor at Salon Magazine, hours clearing up the mess.

• The Electronic Frontier Foundation (EFF), on the cutting edge of Internet policy, installed filters that tagged its own newsletter as spam, according to Brad Templeton, the group's chairman.

• Susan Hough, editor in chief of Seismological Research Letters, had one submitted article trapped in her spam filter for nearly a week. The reason? The e-mail came from a Mexican domain, included a large attachment, and was titled "Submission" - a word the filtering software identified as smut.

As individuals and companies scramble to block the growing deluge of junk e-mail, known as spam, they're running into the opposite problem. Legitimate messages are being blocked before they reach their final destination. The problem: misconfigured spam filters.

The root of the problem is the spread of unsolicited e-mail. By April, 70 percent of e-mail traffic will be spam, estimates e-mail security provider Message Labs, up from 50 percent in December. And experts don't believe the new law, CAN-SPAM, will solve the problem. That's why more and more firms are using filtering software.

Unfortunately, the programs don't always work properly. Misconfigured spam filters are not uncommon, experts say, nor are instances of legitimate messages being mislabeled as spam. In fact, 17 percent of e-mail ads requested by users are incorrectly identified as spam by filters, according to Return Path, which provides e-mail services to businesses.

Since such problems, known as false positives, lie at the receiving end, senders of e-mail shouldn't have to change their ways, says Amit Asaravala, editor of Spamotomy (www.spamotomy.com), a website that reviews antispam tools. "False positives are the result of poorly designed or poorly configured spam filters, and it's the receiver's job to make sure legitimate messages don't get caught in that filter.

"That said," he continues, "it is conceivable that a user may be doing something that causes his [outgoing] e-mail to regularly get caught by spam filters. In that case, that person should ask himself, 'Do I remember to include a brief but meaningful subject line on all my messages? Am I putting words in CAPS too often?... Am I sending unusually long or short messages?' "

One solution Mr. Asaravala suggests is to ask recipients to add your name to their "white list," a list of correspondents whose e-mail always clears the spam filter. While, not all filters use white lists, there are other ways to get your messages through:

• Never leave the "From" line blank. Instead, use a line that clearly identifies you for recipients who scan their spam.

• Use the "BCC" feature with caution. Some people set spam filters to delete any e-mail not directed specifically to them.

• Keep distribution lists short. Some filters label e-mail as spam if a list exceeds a given number of recipients.

Don't create subject lines that look like spam, adds the EFF's Mr. Templeton, "since the spam filters are regularly rewritten to match current spams."

If you don't hear back from a correspondent or you get a note that your e-mail was considered spam, try sending the note again with a different subject line. If your messages continue to be blocked, contact the recipient to find out if a newly installed spam filter is the problem.

Finally, if you don't receive an expected reply, pick up the phone and ask whether your e-mail arrived. You may find you were sent a reply last week and the real culprit is your own spam filter.