July 13, 2023

The Intricate Dance of Email Deliverability: Unmasking the Hidden Determinants

Email deliverability is a complex subject. The question of what determines email deliverability can be broken down into several factors.

We've currently identified 7 general categories of email deliverability factors. These include:

  • Sender Reputation
  • Engagement
  • Content
  • List Quality
  • Timing & Frequency
  • Personalization & Targeting
  • Mobile Optimization
Let's explore each one of these in turn.
Sender Reputation
Sender reputation is a general term that encompasses how good you are as an email sender. A high sender reputation is correlated with high email deliverability. On the flip side, a bad sender reputation is highly correlated with low email deliverability, as it makes getting into the inbox much harder.

Sender reputation isn't a cut and dry score, but rather a combination of various measurements of IP reputation, domain reputation, blacklist presence, and other factors.

Moreover, a clean and proper setup of your email authentication records is also important in setting the foundation to build a good sender reputation.

Sender reputation flows to identifiers of your business or brand as an email sender, and those two identifiers are largely centered around the sending IP(s) and sending domain.

Sender IP Reputation
Whenever your email message gets sent out, it always has an originating IP address that is the sender IP.

This IP carries a reputation, known as its sender IP reputation, based on the history of messages that originated from the IP address. Factors like age of IP, historic volume, blacklist presence, passing authentication, and more combine to determine the overall picture of the sender IP's reputation.

Generally speaking sender IP reputation is positively impacted by:

  • Older IP address
  • Higher volume of messages sent
  • Consistent volume of messages
  • Low spam complaint rates
  • Low bounce rates
  • Few spam trap hits
  • Proper SPF / DKIM / DMARC records
  • Low presence on blacklists
All of these factors play their part in creating a high-reputation sender IP.

Sender Domain Reputation
Domain reputation are affected largely by similar factors as sender IP reputation. Over time, the receiving inboxes have shifted to weighing domain reputation more heavily relative to sender IP reputation. This is partially because switching IPs has become much easier, whereas switching domains is harder for a sender. Thus, the sender domain serves as a better identifier of the email message sender.

One of the key deliverability factors is user engagement levels. A user's email engagement refers to the set of actions the user takes towards a sender's email messages. Specifically, inboxes are looking at the history and ratios of both positive user engagement and negative user engagement to make deliverability decisions.

Positive email engagement signals include:

  • Opening emails
  • Click links in emails
  • Starring/Marking as Important
  • Replying to emails
  • Forwarding emails
  • Adding sender to whitelist

On the contrary, negative email engagement signals include:

  • Marking emails as spam
  • Deleting without reading
  • Not opening emails
  • Not clicking emails
  • Bouncing emails

Given this set of user actions' role in deliverability, it's highly important to make sure your emails are generating a high ratio of the positive user engagement signals and a low ratio of negative user engagement signals.

To do so requires you to start with list segmentation and matching the relevant content to the specific target segments. Also, you need to optimize your list acquisition and cleansing tactics for good subscribers, not just high volume of subscribers.

We've seen email deliverability rates fluctuate significantly (both positively and negatively) based on user engagement trends, so this is definitely a very important factor to keep track of on your quest for perfect email deliverability.

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