Email Reputation Clusters and Fingerprinting

March 20, 2020
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Email Reputation Clusters and Fingerprinting

I spend a lot of time talking to senders about things like IP, domain, and content reputation. In doing so, it can be very easy for senders to get overly focused on singular elements of their mail program when things go wrong.

For example, it can be very tempting to try to improve your reputation by changing out IP addresses or domains that have less than stellar reputations. You might see some change in results in the short-term, but this can be misleading and–in the long-term–quite damaging.

When I talk to senders about how they use their sending infrastructures (their IP addresses, domains, authentication, etc.), I find it most helpful to start with the concept of "fingerprinting" or "clustering." While there might be some differences in how some people think of these terms, to me they are describing virtually the same thing: the establishment of sending reputation attributed to multiple and combined data points.

How clustering and fingerprinting affects your deliverability

Mailbox providers use very sophisticated machine learning to make decisions about what to do with the email they receive. Those algorithms take signals–like opens and spam reports, time spent reading messages versus simply deleting, and more–and apply them to a cluster of data points to create an overall fingerprint of wanted versus unwanted email.

If mailbox providers see a particular cluster of elements that typically signal unwanted email, that cluster of elements will build its own negative reputation.

A simple cluster example

Imagine an email campaign that generates a lot of spam complaints. Inbox providers will examine the following elements:
  • That campaign’s from address
  • Email authentication domains
  • IP address
  • Subject line
  • Template/design
  • Content
The inbox provider will not only look at each element individually but also if any combination of two or more of those elements correlates to low engagement and spam complaints.

The more elements they consistently see generating these results as a “cluster,” the more that cluster builds its own reputation fingerprint. This allows mailbox providers to be much more accurate in their filtering than in times past.
Elements outside of your control can also be included in reputation clusters.
Actions of other senders in the world can also cause certain types of content to gain their own negative (or positive) reputations in the eyes of mailbox providers. If a certain topic or industry is particularly abused by spammers and scammers, those general topics and industries can, themselves, become less trusted by mailbox providers.

A good way to understand this concept is to periodically look through your spam folder. I’d be surprised if you don’t quickly start seeing patterns and clusters of signals yourself.

How to optimize your email infrastructure

Understanding how mailbox providers cluster elements of your email program to create reputation fingerprints will make you a more strategic sender. For example, if you send marketing and transactional emails, we highly recommend using two distinct mailing infrastructures for each email stream.

The reason for this is simple: those transactional messages are critical to your business and customer base. Marketing messages are less engaging to recipients (understandably so) than transactional messages like password resets or receipts.

You would not want spam complaints or low engagement with marketing emails to cause inboxing issues for your transactional emails.
This will create distinct clusters for your mail streams–with distinct reputations.
Understanding clustering also helps you as the sender make more meaningful changes should you run into either inboxing or delivery problems.

Let's say suddenly one of your IPs is added to a deny list and causing delivery disruptions for your email. Instead of changing the IP address (where the change itself can actually be a negative signal to spam filtering providers),  look more holistically at your email program and all its elements. Doing so can likely reveal what needs to be changed to produce a more positive fingerprint for the cluster of sending elements you are using.

If you have evidence that spam complaints are causing you sending reputation issues, a new IP will never fix that problem. Instead, look for reasons your recipients would feel that what they are receiving is not what they signed up for and adjust your processes accordingly.

If recipients simply aren't engaging with your content, then you will likely want to spend effort on crafting more engaging content, offers, and subject lines. Or, perhaps you want to more aggressively sunset addresses that have gone a long time without engaging with your messages.

Finally, if you are in an industry that may have a broader reputation issue that does not mean you can’t get your emails to the inbox. Senders in the employment industry, for example, sometimes have a harder time than other senders getting their messages to the inbox. That's because there are a lot of senders that send employment content who also generating a lot of spam complaints.

Understanding clustering allows you to craft your email campaigns (no matter your industry) so you are creating strong clusters of positive signals. Authentication best practices, consistent sending habits, and high engagement will all help you send the right signals to the inbox providers.  


Senders don't run into problems simply because of a “bad” IP or domain or sending infrastructure. Senders run into delivery or inboxing issues because their email sending patterns are generating signals that match a fingerprint of unwanted mail in the mailbox provider's eyes.

Infrastructure changes in response to most inboxing issues can only, at best, produce short-lasting positive results. Since new combinations of sending elements create new clusters with no sending reputation, changing out sending elements rather than addressing the underlying problems facing an email program can actually cause more delivery and inboxing hardship.

How recipients react to the email you send them determines the reputation of all of the sending elements you are using. Focus your efforts on pleasing your subscribers and structuring your email program so that you control those clusters and more clearly demonstrate that recipients want your emails.

If you are interested in how Twilio SendGrid's email experts can help you optimize your email program or repair delivery or inboxing issues you are experiencing, contact us for information on our expert services offerings.

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