Ninety seven percent of sending IP addresses’ reputations are so bad that e-mail box providers are likely to block their messages, according to a study by e-mail deliverability concern Return Path.

Moreover just 0.9% of sending IP addresses scored well enough that their e-mail is likely to be delivered, the company determined.

Return Path’s Sender Score Reputation Monitor tracks more than 20 million IP addresses provided by ISPs, filtering services and other sources, and assigns each address a 1 to 100 score like a credit report. The service uses six criteria: complaint rates, volume of e-mail sent, unknown user rates (where the address holder no longer exists), unsubscribe practices and how sound the sender’s infrastructure is.

Senders with scores above 70 will likely get their e-mail delivered; those below 30 likely won’t.

The good news: most commercial marketers’ IP addresses fall in that 0.9% that will likely get their e-mail delivered. The bad news: The vast majority of commercial marketers are much closer to 70 than 100, and will experience deliverability problems from time to time as a result, according to Return Path.

“Most marketers are between 60 and 80,” said George Bilbrey, general manager of Return Path’s delivery assurance solutions unit. “Most marketers are in the gray area. The question is: How gray are you and how can you get yourself to a lighter shade of gray?”

The vast majority of the highest scoring IP addresses are those of corporate accounts used by people who don’t send a whole lot of e-mail and don’t spam, according to Return Path. The bulk of those scoring below 30 are those of spammers. Return Path’s numbers are in line with recent ISP reports that 80% of incoming e-mail is spam.

“Commercial e-mailers are competing at the gateway with a lot of crud e-mail,” said Bilbrey. “It’s no wonder there’s a false-positive problem.”

The sender’s reputation is the No. 1 measure ISPs use to determine whether or not to block incoming e-mail, not content as most marketers think, said Bilbrey. Also, recipient complaint rates are the No. 1 factor e-mail box providers use to determine a sender’s reputation.

Other reputation factors include whether or not the sender is hitting spam traps, how many unknown users the sender’s e-mail is hitting, and how well configured the sender’s infrastructure is.

“There’s a great deal of time and effort being spent optimizing the creative and the message to make sure the mail gets delivered, and there is some value to that,” said Bilbrey. “But reputation generally is the No. 1 factor; content is a distant No. 2.”

Also, just because a marketer uses an e-mail service provider doesn’t mean their reputation is stellar, according to Bilbrey. E-mail service providers’ IP address reputations are determined by their clients’ behavior, he said.

Until recently, monitoring one’s own e-mail reputation has been difficult, said Bilbrey. But besides services like Return Path’s Sender Score Reputation Monitor, ISPs are also increasingly making reputation data available, he said.

“It’s becoming easier for marketers to determine what their reputation is,” he said.

To improve their reputations, marketers should focus on lowering complaint rates, making sure their lists are clean and that they aren’t mailing to spam traps, and making sure their sending infrastructure is sound, said Bilbrey.

Ensuring a sound sending infrastructure involves a host of technical issues, he added.

“Those are the things that move the needle in deliverability,” he said.