Contrary to the widely held belief, email message content is not a major cause of deliverability challenges for most email marketers, according to the Lyris EmailAdvisor ISP Deliverability Report Card for 1Q07, reports MarketingCharts.

Moreover, most of the largest US-based ISPs have the lowest rates of delivering email to the inbox, according to Lyris, a subsidiary of J.L. Halsey.

According to the report, "two frequently triggered Spam Assassin rules generated content filter point scores of significance…. The first rule cautions against heavy use of images, which can increase spam scores up to a full point and render poorly in email clients with image blocking enabled. The second problem, sending messages with a 'From Name' composed of numbers or symbols rather than an actual name, can also increase the likelihood of the message being flagged as spam and ending up in users' junk/bulk folders."

However, "it's an oversimplification to place blame primarily on content filters when a campaign has poor returns, when in fact most delivery challenges are due to subscriber feedback" - such as complaints by recipients who mark a message as "spam" in their email clients - said Stefan Pollard, Director of Consulting Services at J.L Halsey's EmailLabs.

Of the 25 U.S. ISPs tracked by the EmailAdvisor Report Card, several leading providers rank among the top 10 domains with the highest rates of delivery to the junk folder: Gmail (third with 28 percent), Yahoo (fourth with 19 percent), and Hotmail (sixth with 16 percent).

AOL ranked 14th, with a junk delivery rate of only 2.33 percent.

MarketingCharts provides more data.