Reputation, Not Content, Key To E-mail Deliverability: Study

If marketing e-mails aren't reaching targets' in-boxes, message content may be the least of the reason. According to a new study from Return Path, the reputation of a sending server's IP address and whether messages hit spam traps or other invalid e-mailboxes are key determinants for e-mail deliverability.

The study offers a roundup of the most common stumbling blocks for e-mail marketers. Content filtering, according to Return Path director of professional services Tom Sather, happens "late in the game" of filtering techniques.

"The receivers have seen a high false positive rate with content filters," Sather says. "They don't rely on it as much."

The receivers—the ISPs (Internet service providers) and mailbox providers, as well the mailbox owners themselves—use a variety of reputation-based criteria, according to Sather. In the cases of the ISPs and mailbox providers, these can include whether an IP address is known for sending messages to deactivated e-mail addresses, or addresses that have been set up specifically as spam traps. Messages sent to these "unknown user" addresses can raise the likelihood of being labeled spam, increasing the chance they'll be diverted before reaching an e-mailbox.

Individual mailbox owners can further damage a sender's reputation by marking e-mails as spam, even if they had previously requested to be contacted. These actions are among the most damaging to a marketer's e-mail reputation: Even a 0.1% complaint rate can knock a reputation score, as calculated by Return Path, from 100 to the 81-90 range.

Complicating matters further, there is no uniform set of deliverability rules among the ISPs. Their thresholds within each reputation element— messages sent to dead e-mailboxes, user complaints and the like—vary.

Deliverability ranges considerably based on a mailer's sender reputation score. Those with top scores—between 91 and 100—can reasonably expect 88% of their messages to make their way past the various hurdles and into recipient inboxes. But those with sender scores of, say, between 61 and 70 can expect up to one quarter of their messages to be blocked, according to Return Path's analysis of ISP deliverability data.

Sender reputations are quick to be soiled, and not so easy to repair. "A spammer can't just get a new IP address and get a good reputation," says Sather. ISPs tend to "treat [new IPs] like a dog on a short leash" until they can determine whether messages are spam or legitimate mail. "They'll be limiting the number of messages [a marketer] can send to their system. During that time, they'll be looking at metrics such as complaint rates, spam trap hits and unknown user mailboxes contacted to get a picture of [a marketer's] reputation."

Even benign neglect can affect a marketer's ability to get delivered. A preponderance of messages which are ignored, such as consistently not being opened, not having links clicked or being deleted without review can damage a sender's reputation.

For all this, established marketers are having a slightly easier time getting their messages delivered, Sather says. They are getting more knowledgeable about deliverability metrics and reputation concerns. And the various mailbox gatekeepers are using e-mail authentication services—anti-phishing tactics which attempt to confirm that mail is genuinely from the marketer it claims to be from.

That said, "I think that people will always run into problems," Sather says. "There will always be new people in the industry who don't understand e-mail. And upper management will want marketers to grow lists aggressively, which may make [marketers] look like spammers. Or they may increase their mail volume during holidays, which may increase complaints and make them look spammy."