How does email reputation work?

A little bit of email reputation history

Since reputation systems became the de-facto method of spam filtering in about 2010, the focus was mainly on IP reputation, with domain reputation lagging. However, this has changed significantly in the last few years; IP reputation is less important than the reputation of domains and content for inbox placement.

One of the reasons IP reputation is falling behind is the advent of IPv6. It’s HUGE. It has 340,282,366,920,938,463,463,374,607,431,768,211,456 IP addresses available; enough IP addresses for every single device in the world to have its own, and there would still be IPs left over.

This glut of IPs means that cybercriminals can afford to burn IPs like paper (and they do), and therefore we cannot solely rely on blocking by IP to protect users. IPv4 is still the default for email, but it’s running out very quickly, and spam filters need to be ahead of the game.

Today’s email reputation reality

In the modern email ecosystem, IP/domain reputation and recipient engagement are the elements that drive email reputation. The days of “whitelisting” are long gone; we are unaware of any ISP that offers allowlisting in any form today.

Reputation systems are designed to automate spam filtering and enable ISPs to react to reputational changes in a rapid and agile manner. Another point to note is that they are agnostic:

• They do not care about business models.
• They do care about end-user engagement.
• They do care whether or not mail is authenticated correctly.

What affects email reputation?

Reputation is composed of an unknown number of variables that ISPs or reputation providers like Spamhaus do not reveal. But some general components are known, and you can manage them with appropriate address acquisition and data hygiene.

• Spamtrap hits – A spam trap is an email address traditionally used to expose illegitimate senders who add email addresses to their lists without permission. Still, spamtraps are also very effective in identifying email marketers with poor data collection and list management practices. Find out more.
• Complaint volumes – Monitoring complaints is an essential part of the reputational pie, so keeping them as low as possible should be every marketer’s goal. To do this, you must consider several things. Find out more.
• Engagement metrics – Engagement is useful for measuring how a marketing program is performing, and has typically been measured by recording clicks, opens*, and purchases. Find out more.
• Management of bounces/invalid addresses – Bounce management needs to be handled quickly to ensure that you are taking the necessary actions to ensure your mailing list is clean. Find out more.
• Consistent mail stream volumes. Some ISPs are more reactive to this than others. ISPs are far more concerned about botnet spam than marketing mail. Sudden changes in mail volume are typical of infected hosts, and ISPs react accordingly. “Bursty” email streams will degrade even well-established reputation with the major freemail ISPs. Find out more.

What drives inbox placement?

Today, inbox placement is dynamic and almost entirely dependent on IP/domain reputation, which is re-calculated exceptionally quickly in response to end-user reactions and thousands of other heuristics, so the way an email stream is treated can change by the moment.

Spam-folder placement is also driven by reputation and user-defined mailbox preferences.

Preparing for the launch of a new IP or domain

Reputation is established during the IP or domain warmup/ramp-up phase – this makes the preparation for the warmup process critical.

It is very much like going on a first date: first impressions matter a great deal and linger for a long time.

1. Plan & select: To prepare for the launch of a new IP or domain, you need to plan the deployment, carefully selecting a set of highly engaged recipients for the initial mailings. These should then be sent in a thoughtful and measured fashion until you reach production volume.
2. Continual improvement: This is a crucial period during which every iteration needs to be meticulously studied, adjustments made, and issues corrected – no matter how painful those corrections may be, i.e., how many potential recipients you need to remove from your segmentation.

Increasing rates of volume and speed should depend on the results of each previous deployment. This means that today’s email marketers should be focusing on engagement as much (or more!) than on IP reputation. The days of ‘”batch and blast” are over, but the good news is that the more engagement an email receives, the better deliverability gets, and this has a positive knock-on effect on a sender’s ROI. It is not instant and can be very frustrating, but it is worth it.

Critical learning when it comes to email reputation

It is much, much easier to drive reputation down than it is to fix a damaged one – this behavior was created by design, and there is no override! Don’t try and short-cut building good reputation; otherwise, you’ll be spending a lot of time, effort, and potentially money rebuilding it.

Next in our series, we’ll be looking at the legalities around address acquisition!

* In the advent of Apple’s Email Privacy Protection, measuring “clicks” is now a less accurate measurement to rely on.