• by Wendy Davis  @wendyndavis, April 4, 2006

Slightly more than one in five marketing e-mails--20.5 percent--didn't get delivered in the second half of last year, down slightly from 21 percent in the first six months of the year and 22 percent in 2004, according to a new report by Return Path.

For the report, Return Path examined more than 117,000 permission-based e-mail campaigns sent through 28 different Internet service providers and the three leading corporate filtering systems.

The report found that non-delivery rates varied greatly by service provider. Excite filtered our 42.9 percent of messages, while Gmail filtered 40.4 percent, Lycos didn't deliver 33.8 percent, and Adelphia failed to deliver 31 percent of messages. On the other end of the spectrum, EarthLink filtered out just 7.8 percent of e-mails, while Mac.com, Compuserve, and USA.net all filtered out less than 10 percent (8.1 percent, 9.4 percent, and 9.9 percent, respectively).

AOL--which recently announced a controversial plan to assure delivery to senders who pay to be certified by Goodmail--didn't deliver 12.4 percent of messages.

As for corporate filters, MessageLabs didn't deliver 30.5 percent of messages, Postini failed to send 24 percent, and Brightmail blocked 21.5 percent.