According to the newest report from ReturnPath, sender reputation causes email delivery issues 83 percent of the time. Content is only a secondary factor, much below reputation when email gets blocked or junked.

In a test during August 2006, nearly 20 percent of legitimate commercial email did not get delivered into the inbox. The study shows that 77 percent of delivery issues occur because of the sender’s email reputation. An additional 6 percent are triggered by the reputation of domains included in the email content.

Content only plays a part in 23 percent of delivery issues, and only 17 percent being related to factors such as words, fonts, images or spelling.

The study also reveals that out of the 21 major North American ISPs, five of them showed 100 reputation to be 100 percent of the reason behind non-delivery. Download the report (registration required) for a nicely illustrated chart and table.

Note: The data were based on a study by ReturnPath on more than 550 email campaigns sent by its Sender Score Monitor clients that had Inbox delivery rates of less than 90 percent. While the emails were resent using a clean IP address, they were actually blocked or bulked previously by the same ISPs.

Also keep in mind that ReturnPath is providing SenderScore, a sender reputation monitor service.