• by Gavin O'Malley  @mp_gavin, October 13, 2005

The blocking of permission-based e-mail by users' Internet service providers and Web-based e-mail providers remained just as big a problem this year as it was last year, according to a recent Return Path e-mail deliverability study.

Mistaking legitimate e-mail for spam, ISPs, and Web-based e-mail providers failed to deliver 21 percent of permission-based e-mail to consumer inboxes during the first half of this year, compared to 22 percent during all of last year.

The study examined 140,000 marketing and transactional campaigns sent by clients via Return Path's Delivery Assurance Mailbox Monitor service between January and June 2005.

While an average of 21 percent of e-mails were blocked or filtered and did not reach consumers' inboxes across all mailers, the levels of blocking and filtering varied by mailer from a low of 1 percent to a high of 54 percent, according to the study. Moreover, on an ISP-by-ISP basis, the non-delivery rates ranged from a low of 8 percent to a high of 39 percent.

Companies saw the best delivery success at Mac.com, which only blocked or filtered 8 percent, and Earthlink and USA.net, which each blocked 10 percent. Excite and Gmail blocked or filtered the most permission-based e-mail--39 percent--followed by MSN with 33 percent, and Hotmail, which blocked or filtered 32 percent of permission-based e-mail.

Looking at campaigns for a broad sample of clients for whom Return Path monitors deliverability, as well as long-term clients in particular, the study found that the average non-delivery rate for companies which have used Return Path for 6 months or more improves to just 6 percent, with a range of 1 percent to 17 percent.

George Bilbrey, general manager of Return Path's Delivery Assurance division, said companies might have to tweak their e-mail programs to increase their delivery rate. "ISPs and Web-based e-mail providers are utilizing a wide range of filtering technologies to combat spam," Bilbrey said. "Companies have to adjust their e-mail program, or work with an outside service, to ensure their e-mail campaigns have the highest deliverability rate possible."