Gmail's spam filter doesn't just look at your email content. It watches what happens after delivery. Do recipients open your emails? Click links? Reply? Move them out of spam? Or do they ignore them, delete them unread, or hit the spam button?
This behavioral data—engagement—has become one of the most important factors in email deliverability. ISPs use it to determine whether your emails are wanted. High engagement signals valuable content; low engagement signals spam. Understanding and optimizing engagement is essential for email success.
What counts as engagement
Engagement encompasses all the ways recipients interact with your emails, both positive and negative.
Positive engagement signals include opening the email, clicking links, replying, forwarding to others, moving from spam to inbox, adding you to contacts, and starring or flagging for follow-up. These actions tell ISPs that recipients want your email.
Negative engagement signals include deleting without reading, marking as spam, unsubscribing, and ignoring emails consistently. These tell ISPs that recipients don't value your content.
Neutral or ambiguous signals include reading without clicking (engaged but not compelled to act) and archiving (valued enough to keep but not act on). ISPs interpret these contextually.
The balance of positive to negative engagement shapes your sender reputation. Lots of opens and clicks with few complaints builds reputation. Lots of ignores and spam reports destroys it.
How ISPs use engagement data
Major email providers, especially Gmail, heavily weight engagement in their filtering decisions.
Gmail tracks engagement at multiple levels: individual recipient behavior with your emails, aggregate behavior across all recipients, and how your engagement compares to similar senders. All of this feeds into whether your next email reaches the inbox.
The feedback loop is powerful. Good engagement leads to better inbox placement, which enables more engagement, which further improves placement. Bad engagement leads to spam folder placement, which prevents engagement, which confirms the spam classification.
This creates winner-take-all dynamics. Senders with engaged audiences get increasingly better treatment. Senders with disengaged audiences spiral downward. The middle ground is unstable—you're usually trending one direction or the other.
Engagement signals are relative, not absolute. Gmail doesn't expect 50% open rates from everyone. It compares your engagement to what's normal for your type of sending. A newsletter with 25% opens might be healthy; a transactional email with 25% opens might indicate problems.
Measuring engagement
Different engagement metrics serve different purposes.
Open rate is the traditional engagement metric but increasingly unreliable. Privacy features inflate opens; image blocking deflates them. Use open rates for trends and comparisons, not absolute measurement.
Click-through rate is more reliable because clicks require deliberate action. It measures active engagement—recipients interested enough to take action. This is often the best single engagement metric.
Click-to-open rate measures engagement depth. Among people who opened, how many clicked? This isolates content effectiveness from subject line effectiveness.
Reply rate matters for emails that invite responses. Replies are strong positive signals and indicate genuine two-way engagement.
Unsubscribe rate measures negative engagement. Some unsubscribes are healthy (self-selection), but rising rates indicate problems.
Complaint rate is the most damaging negative signal. Even small complaint rates hurt deliverability significantly.
Time-based patterns add nuance. Do people engage immediately or days later? Do they engage consistently or sporadically? These patterns inform sending strategy.
Engagement scoring
Many email platforms calculate engagement scores that combine multiple signals into a single metric per subscriber.
A typical scoring model might assign points for recent opens, clicks, and purchases, while subtracting points for time since last engagement. The result is a score indicating how engaged each subscriber is.
Engagement scores enable segmentation. You can identify your most engaged subscribers for special offers, your least engaged for re-engagement campaigns, and everyone in between for standard communication.
Scores should decay over time. A subscriber who clicked last week is more engaged than one who clicked last year. Build time decay into your scoring model.
Different engagement types might warrant different weights. A purchase indicates stronger engagement than an open. A reply indicates stronger engagement than a click. Weight accordingly.
Why engagement declines
Understanding why engagement drops helps you prevent and reverse it.
List age is the primary factor. New subscribers are typically most engaged. Engagement naturally decays over time as interests change, inboxes fill, and the novelty of your content fades.
Content relevance drives engagement. If your emails don't provide value, people stop engaging. This seems obvious but is often overlooked. The solution to low engagement is often better content, not better tactics.
Sending frequency affects engagement in both directions. Too frequent, and you fatigue subscribers. Too infrequent, and they forget who you are. Finding the right cadence for your audience matters.
Inbox competition has increased dramatically. Your emails compete with hundreds of others for attention. Standing out requires compelling subject lines and consistent value delivery.
Deliverability problems cause engagement drops. If emails go to spam, engagement plummets—not because recipients don't want them, but because they never see them. Always check deliverability when engagement drops.
Improving engagement
Several strategies can improve engagement across your email program.
Segment by engagement level. Send your best content to your most engaged subscribers. Send re-engagement campaigns to declining subscribers. Consider sunsetting chronically unengaged subscribers.
Optimize for the inbox. Subject lines determine whether emails get opened. Preview text provides additional context. Sender name affects trust. These elements deserve ongoing testing and optimization.
Deliver genuine value. Every email should give recipients something useful—information, entertainment, offers, tools. If you can't articulate the value of an email, don't send it.
Respect preferences. Let subscribers choose frequency and content types. Honor those preferences. People who control their experience engage more than those who feel spammed.
Make engagement easy. Clear CTAs, mobile-friendly design, fast-loading content. Remove friction between wanting to engage and actually engaging.
Time your sends appropriately. Test different send times for your audience. The best time varies by audience, content type, and geography.
The engagement-deliverability connection
Engagement and deliverability form a feedback loop that can spiral up or down.
High engagement improves deliverability. ISPs see that recipients want your email and route more of it to the inbox. This enables more engagement, further improving deliverability.
Low engagement hurts deliverability. ISPs see that recipients ignore or complain about your email and route more to spam. This prevents engagement, confirming the negative signal.
Breaking a negative spiral requires intervention. You can't just keep sending and hope engagement improves. You need to reduce volume, focus on engaged segments, improve content, and gradually rebuild.
Maintaining a positive spiral requires vigilance. Engagement naturally decays; you need to continuously earn it. Complacency leads to decline.
Engagement for transactional email
Transactional emails have different engagement dynamics than marketing emails.
Expected engagement is higher. Password resets, order confirmations, and shipping notifications are emails people want and expect. Open and click rates should be significantly higher than marketing benchmarks.
Low engagement indicates problems. If transactional email engagement is low, something is wrong—emails might be going to spam, arriving late, or being sent to wrong addresses.
Engagement still matters for reputation. Even though transactional emails are "expected," ISPs still track engagement. Consistently ignored transactional emails can hurt your sender reputation.
Measure completion, not just clicks. For transactional emails, the goal is usually completing an action (resetting password, tracking package). Measure whether that action happens, not just whether the email was clicked.
Frequently asked questions
What's a good engagement rate?
It varies by email type and industry. For marketing emails, 15-25% open rates and 2-5% click rates are typical. For transactional emails, expect much higher. Compare to your own history and industry benchmarks.
How quickly does engagement affect deliverability?
Effects accumulate over time. A single low-engagement campaign won't tank your reputation. Consistently low engagement over weeks or months will. Similarly, improvement takes sustained effort.
Should I remove unengaged subscribers?
Eventually, yes. Chronically unengaged subscribers hurt your metrics and increase spam trap risk. But try re-engagement first. Remove subscribers who don't respond to re-engagement efforts after a defined period.
Does engagement matter for small senders?
Yes, though the dynamics differ. Small senders have less data for ISPs to evaluate, so each engagement signal carries more weight. Maintaining high engagement is important at any scale.