Study: Spam Filters Often Lose E-Mails

A new study attempts to quantify missed bulk mailings. Return Path, a company that monitors e-mail performance for online marketers, found that nearly 19 percent of e-mail sent by its customers never reached the inboxes of intended recipients.

The figure, for the last half of 2003, is up 3.7 percentage points from the same period in 2002.

In some cases, the messages weren't delivered at all; in other cases, messages wound up in spam folders that are rarely checked. Though technical glitches can also cause mail to disappear, Return Path blames most of the deletions on spam filters.

Major e-mail service providers, aware that filters can falsely tag messages as spam, have been working on better tools to verify senders of e-mail, so that legitimate mailings can get through.

Promotions and greeting cards were the types of messages most likely to disappear, the study found.

The study was based on a snapshot of messages sent by 100 Return Path customers. Return Path set up test mailboxes with 18 major Internet service providers and monitored about one-fourth of the 120,000 marketing campaigns from those customers.