How do Internet Service Providers track email engagement and its impact on deliverability?
Matthew Whittaker
Co-founder & CTO, Suped
Published 15 Apr 2025
Updated 19 Aug 2025
7 min read
Email deliverability is a complex landscape, and one of the most crucial elements influencing whether your messages land in the inbox or the spam folder is how Internet Service Providers (ISPs) perceive your engagement. They are constantly monitoring how recipients interact with your emails to gauge your trustworthiness as a sender.
Understanding what ISPs track and why it matters is fundamental to maintaining a strong sender reputation and ensuring your emails reach their intended audience. It's not just about getting the email delivered, it's about getting it into the primary inbox.
How ISPs measure engagement signals
ISPs, such as Google (Gmail), Microsoft (Outlook/Hotmail), and Oath (Yahoo Mail, AOL), employ sophisticated algorithms to analyze how their users interact with incoming emails. This engagement data is a primary factor in determining your sender reputation score. A high score means your emails are more likely to reach the inbox, while a low score can lead to messages being routed to spam or blocked entirely.
These algorithms consider a wide array of signals, not just opens and clicks. They aim to understand the overall recipient sentiment towards your emails. For example, if many recipients consistently ignore, delete without opening, or mark your emails as spam, it signals to the ISP that your content may be unwanted or irrelevant. Conversely, positive interactions reinforce your legitimacy.
It's important to note that the exact weighting of each engagement metric varies between ISPs and is constantly evolving. What works for Yahoo Mail might not be identical to Outlook. However, the general principle remains: senders who consistently receive positive engagement are rewarded with better inbox placement.
Key engagement metrics monitored by ISPs
The ISP's ability to track engagement largely depends on whether they control the mailbox interface. Webmail providers, like Gmail, Outlook.com, and Yahoo Mail, have comprehensive visibility into user behavior within their platforms. They can track a nuanced range of interactions beyond what a sender's own Email Service Provider (ESP) might capture.
Open rates: ISPs track when an email is opened. While ESPs use tracking pixels for this, ISPs have a more direct view, especially if images are blocked, they can still infer an open from other interactions.
Click-through rates: When a recipient clicks a link within an email, ISPs record this. This is a strong positive signal.
Replies and forwards: These actions indicate a high level of engagement and are very positive signals to ISPs.
Moving to inbox: If a user moves an email from the spam folder to the inbox, it's a powerful positive signal, directly overriding an initial spam classification. This is critical for recovering from accidental spam placements.
Adding to contacts: When a recipient adds your sending address to their contact list, it's a clear indication of trust and a desire to receive your emails.
Conversely, negative engagement metrics are equally, if not more, impactful. These include spam complaints (the most damaging), deletions without opening, marking as junk, or moving emails to the trash folder. ISPs track these signals closely to protect their users from unwanted mail, as highlighted in resources on email deliverability.
Webmail vs. enterprise ISP tracking
It's a common misconception that all ISPs track engagement in the same way, or to the same extent. While major webmail providers heavily rely on engagement, the approach for enterprise-level mail servers (like those running Google Workspace or Microsoft 365) can differ significantly.
Webmail providers
Platforms like Gmail and Outlook.com have direct access to a user's interactions within their ecosystem. They track every click, open, delete, forward, and spam report directly. Their sophisticated filtering systems, like Gmail's own algorithms, are heavily influenced by individual and aggregate engagement patterns.
They prioritize user satisfaction above all else, so if users consistently engage positively with a sender, that sender is rewarded with better inbox placement. Conversely, poor engagement quickly leads to filtering into the spam folder.
Enterprise ISPs and internal filters
Enterprise mail systems often rely more on traditional reputation metrics like spam traps, bounce rates, and direct user complaints, rather than nuanced engagement signals like opens or clicks. Their primary goal is to block outright spam and protect corporate networks.
While some enterprise filters may incorporate engagement factors over time, their immediate concern is often mail volume, sender authentication (SPF, DKIM, DMARC), and blocklist (or blacklist) presence. A single complaint from a C-level executive can be far more damaging than dozens of ignored emails from standard users.
The distinction is crucial for B2B senders, who often target enterprise inboxes. While good engagement practices are always beneficial, authentication and list hygiene (avoiding spam traps and managing bounces) tend to be paramount for these recipients.
The impact of engagement on deliverability
Poor email engagement directly correlates with lower deliverability. When ISPs observe low open rates, high unsubscribe rates, or frequent spam complaints, they interpret this as a signal that your emails are not valued by recipients, or worse, are unwanted. This negative feedback leads to a diminished sender reputation.
Once your reputation declines, ISPs are more likely to filter your emails to the spam folder, or even reject them outright. This creates a vicious cycle: lower inbox placement means fewer opens and clicks, further eroding your engagement metrics and reputation. This is why understanding email deliverability is so critical for email marketers.
Best practices for positive engagement
Segment your audience: Send relevant content to specific groups, improving the likelihood of interaction.
Personalize content: Address recipients by name and tailor messages to their interests or past behavior.
Optimize subject lines: Make them clear, concise, and compelling to encourage opens without being misleading.
Maintain a clean list: Regularly remove inactive subscribers and hard bounces to reduce negative signals.
Provide clear unsubscribe options: Make it easy for users to opt-out, preventing them from marking your emails as spam instead.
Ultimately, the goal is to consistently send emails that recipients want to receive and interact with. This proactive approach to engagement monitoring and optimization is the most effective way to ensure your emails reliably reach the inbox.
Engagement for enterprise mail systems
For enterprise mail systems, engagement signals are generally less direct. While they don't typically track individual opens and clicks in the same granular way as webmail providers, they do pay close attention to other critical factors that indicate the legitimacy and desired nature of your mail.
Spam complaints: This is universally damaging. Enterprise filters use feedback loops to receive direct reports when their users mark an email as spam. High complaint rates will quickly lead to blocklists (blacklists) or direct rejection.
Bounce rates: A high rate of hard bounces indicates a poor-quality list, which is a strong negative signal to any ISP, enterprise or otherwise.
Spam trap hits: Hitting a spam trap signifies that your list acquisition practices are problematic, resulting in severe damage to your sender reputation.
Authentication status: Proper implementation of SPF, DKIM, and DMARC is foundational. Failing these checks can lead to immediate rejection, regardless of engagement.
While B2B communications might not see the same explicit open/click tracking influencing deliverability as consumer emails, the underlying principle of sending wanted mail is consistent. If corporate users complain, delete without reading, or actively block your domain, it will still have a severe negative impact on your ability to reach those recipients, and potentially others within the same organization.
Views from the trenches
Best practices
Actively segment your subscriber list to send highly relevant content, improving engagement rates naturally.
Implement double opt-in for all new subscribers to ensure they genuinely want to receive your emails, reducing complaints.
Regularly clean your email list by removing inactive subscribers and unengaged contacts.
Common pitfalls
Sending to old, unengaged lists; this leads to high bounce rates and spam complaints.
Purchasing email lists, which often contain spam traps and uninterested recipients.
Expert tips
Use authentication protocols like DMARC to protect your domain from spoofing, which indirectly boosts trust.
Personalize email content and timing to improve relevance and encourage positive recipient interaction.
Provide an easy and clear unsubscribe link to reduce spam complaints from users who no longer wish to receive your emails.
Expert view
Expert from Email Geeks says that how clicks generate open events, whether unsubscribe clicks are tracked, and if unique or gross metrics are reported can vary widely across platforms.
2018-11-07 - Email Geeks
Expert view
Expert from Email Geeks says that engagement data is primarily used by webmail providers like Gmail, Microsoft, and Oath (Yahoo, AOL), while other filters focus less on it.
2018-11-07 - Email Geeks
Mastering email deliverability through engagement
Understanding how ISPs track email engagement and its direct impact on deliverability is no longer optional for senders. It's a fundamental aspect of successful email marketing and communication. By focusing on quality content, engaged audiences, and best practices, you can build a positive sender reputation that ensures your emails consistently reach the inbox.
Remember, every interaction a recipient has with your email, positive or negative, contributes to your overall sender score. Prioritize delivering value to your subscribers, and ISPs will reward you with better email deliverability.
Google (
Gmail), 
Microsoft (Outlook/Hotmail), and Oath (Yahoo Mail, AOL), employ sophisticated algorithms to analyze how their users interact with incoming emails. This engagement data is a primary factor in determining your sender reputation score. A high score means your emails are more likely to reach the inbox, while a low score can lead to messages being routed to spam or blocked entirely.
Yahoo Mail might not be identical to 
Outlook. However, the general principle remains: senders who consistently receive positive engagement are rewarded with better inbox placement.
