ISPs like Gmail and Yahoo decide where your emails land – primary inbox, spam, or promotions – based on how users interact with them. Engagement metrics, such as opens, clicks, and replies, now play a huge role in email placement. Here’s what you need to know:
- Positive Signals: Actions like opening, replying, clicking on links, or marking emails as "not spam" improve sender reputation.
- Negative Signals: Spam complaints, high unsubscribe rates, deleting emails without opening, or no interaction at all harm your reputation.
- Authentication Matters: ISPs require protocols like SPF, DKIM, and DMARC to verify sender legitimacy.
- Bot Detection: ISPs filter out automated clicks and fake engagement using advanced algorithms.
- Sender Reputation: A strong sender reputation ensures better inbox placement, while poor practices lead to spam filtering.
To improve deliverability, focus on cleaning email lists, sending consistent volumes, and creating content that encourages meaningful interaction. Tools like MailMonitor can help track and optimize your email performance.
How Does Engagement Impact Deliverability? – TheEmailToolbox.com
Engagement Metrics ISPs Track
Internet Service Providers (ISPs) closely monitor recipient behavior to decide whether your emails land in the inbox or get flagged as spam. Knowing what they view as positive or negative signals can make all the difference.
Good Engagement Signals
Delayed open rates often reflect genuine interest. However, tools like Apple Mail Privacy Protection, which preload email content, have forced ISPs to get smarter about identifying real user opens versus automated ones.
Reply rates are another major factor. As Allegrow explains:
Getting a reply to an email is a clear signal of positive engagement for inbox providers. In fact, this engagement signal is so strong that many email experts advise that if a prospect responds to one of the first few emails you send them – they are significantly more likely to receive all the future content you share with them [4].
Even a brief reply, whether it’s a simple thank-you or even an unsubscribe request, can improve your sender reputation.
Click-through rates are another key metric. Matt Schott, Senior Lead Gen Strategist at thunder::tech, highlights their importance:
Click-through rate is a key metric to track in your email marketing software. This, layered with audience size, can really be the foundation of a list that’s ready to be leveraged towards achieving significant business objectives [2].
On average, click-through rates hover around 2.3% across industries, but campaigns with images often see rates about 42% higher.
Other actions that boost your reputation include:
- Forwarding emails or marking them as "not spam"
- Adding the sender to contacts or organizing emails into folders
- Spending more time reading or even printing emails
While these behaviors can help, negative engagement can quickly erode your reputation.
Bad Engagement Signals
Spam complaints are the most damaging signal. Google advises keeping complaints under 0.1% – that’s no more than one complaint per 1,000 emails. As one expert puts it:
Even 1 complaint per 1,000 emails can hurt placement [1].
The main reasons people report emails as spam? Research shows 78% do so because the emails “look like spam,” and 54% because they never consented to receive them.
High unsubscribe rates can signal issues with content relevance or email frequency. In fact, 70% of consumers have unsubscribed from at least three brands in the past three months due to excessive email volume.
Deleting emails without opening them sends a particularly strong negative signal, teaching ISP filters that your messages lack relevance. Carin Slater, Manager of Lifecycle Email Marketing at Litmus, explains:
If an ISP sees that nobody’s interacting with your emails, they’re going to say, ‘Nobody wants this. Must be spam’ [2].
Complete inaction – where recipients neither open, click, nor manage emails – also harms your sender reputation, signaling a lack of interest.
| Engagement Type | Positive Signals | Negative Signals |
|---|---|---|
| Opening Behavior | Opens after a reasonable delay | Immediate automated opens or never opening |
| Click Activity | Selectively clicking on relevant links | No clicks or clicking every link instantly |
| Email Management | Forwarding, saving, or organizing emails | Deleting without opening or ignoring emails |
| Direct Feedback | Replies, marking "not spam", whitelisting | Spam complaints and high unsubscribe rates |
Filtering Out Bot Activity
ISPs also work to separate real user actions from automated behaviors. They analyze timing irregularities and technical identifiers like IP addresses and user-agent strings to detect bots.
John Mac, Senior Growth Consultant at UNIBATT, explains:
Bots tend to click on every link immediately after an email is delivered, often within the first few seconds. Real humans engage at varied times and typically only click on one or two relevant links [3].
For example, one company found its click-through rate inflated by 38% due to bots. After implementing MaxMind filtering, the rate dropped to a more accurate 6.4%, making conversions easier to track.
Melanie Balke, CEO of The Email Marketers, points out two common signs of bot activity:
Every link in the email is clicked (especially including the unsubscribe link — bots love that one) [3]
and
Click timestamps are identical or seconds apart, especially within a second of delivery [3].
Cross-referencing click data with website analytics can help confirm whether high click rates come from real users or bots. If your email platform shows a spike in clicks but your website analytics don’t reflect increased sessions, bots are likely at play.
The methods for spotting bots can vary between B2B and B2C contexts. In B2B scenarios, basic security scanners might click links within 5–60 seconds of delivery, while B2C interactions tend to show more natural, human-like behaviors.
How ISPs Decide Email Placement
ISPs rely on advanced algorithms and engagement data to determine where your emails end up. Knowing how these systems work can help you improve your email strategy and get better inbox placement.
ISP Algorithms and Engagement Scoring
ISPs use real-time scoring to assess the reputation of email senders as messages are received. As Smartlead.ai explains:
"Sender reputation is your email marketing credibility score, as assessed by email service providers (ESPs). It’s based on how trustworthy your sending practices are perceived to be." [5]
These evaluations are powered by AI and machine learning, which analyze factors like IP and domain reputation, reply rates, and email structure. This happens instantly, influencing whether your email lands in the inbox or elsewhere [1][5][6][8][9]. Even when using shared IP addresses, domain reputation still plays a significant role in placement decisions [5][6][8][9].
Different ISP Filtering Methods
Each major ISP has its own filtering process, which is why the same email may show up in different folders depending on the provider. Mailforge.ai highlights this challenge:
"You could have perfect deliverability, and still get zero replies, because Gmail, Outlook, and Apple Mail each have their own filtering logic." [1]
Inbox placement rates vary by provider: Gmail at 87.2%, Yahoo at 86.0%, Apple Mail at 76.3%, and Outlook at 75.6% [1]. Gmail, for instance, uses its Promotions tab system to sort marketing emails into a dedicated folder. This is considered a successful placement for promotional content, as opposed to being flagged as spam [11].
ISPs have also tightened their rules in recent years. By early 2024 and again in May 2025, major providers implemented stricter guidelines requiring bulk senders (those sending over 5,000 emails daily) to maintain spam complaint rates below 0.3% [10].
To help senders monitor their performance, ISPs offer various tools:
- Google Postmaster Tools: Tracks delivery errors, IP and domain reputation, authentication rates, and spam complaints.
- Microsoft SNDS: Focuses on IP reputation and daily spam complaint percentages.
- Yahoo’s Feedback Loop: Sends spam complaints directly to a designated mailbox.
These tools provide insights into how filtering methods impact sender reputation.
How Sender Reputation Works
A strong sender reputation is key to better inbox placement, boosting primary inbox delivery by 45% [1].
Mailgun emphasizes:
"Mailbox providers are judging you – sizing you up as a sender and deciding if your emails are inbox worthy or deserve to end up in spam. Your goal is to stay on their good side, which means thinking about your email sender reputation." [6]
A poor reputation can have serious consequences, including emails being flagged as spam, blacklisting of your domain or IP address, and even suspension of your account by email marketing platforms [5][7][8][9].
Despite its importance, only 25.5% of senders feel they understand their sender reputation, and nearly 70% don’t use available monitoring tools [6]. This lack of awareness puts many at a disadvantage.
To protect vital communications, nearly 50% of high-volume senders (those sending over 50,000 emails monthly) use separate subdomains for marketing and transactional emails. Transactional emails, such as order confirmations, are less likely to be marked as spam [6].
Modern spam filters no longer focus on "spammy language" like using "free" or ALL CAPS. Instead, they prioritize recipient engagement and proper authentication [6][7]. This shift places a heavier emphasis on how recipients interact with emails, making engagement metrics critical to maintaining a strong sender reputation and ensuring successful email placement.
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What Affects Engagement and Deliverability
When it comes to email deliverability, engagement plays a starring role. While sender reputation is critical, other factors – like clean email lists, consistent sending patterns, and managing complaints – work together to determine whether your emails land in the inbox or get filtered out. Let’s break down the key elements.
List Cleaning and Audience Targeting
A clean email list is the foundation of strong engagement. Removing inactive contacts and spam traps not only improves your sender reputation but also ensures you’re reaching people who actually want to hear from you.
Segmenting your audience based on engagement is equally important. Focus on active subscribers – those who regularly open and click your emails. They’re the ones who help maintain a strong sender reputation. Meanwhile, subscribers who consistently ignore your emails should be moved to re-engagement campaigns or removed entirely. Keeping them on your list can drag down your overall performance metrics.
Good list hygiene practices include promptly removing hard bounces and keeping an eye on soft bounces. Repeated soft bounces often indicate inactive or problematic accounts that can harm your reputation over time. A well-maintained, targeted list sends the right signals to Internet Service Providers (ISPs), boosting your chances of making it to the inbox.
Send Frequency, Volume, and Authentication
How often and how much you send matters just as much as what you send. ISPs look for consistency in your sending patterns. As Carin Slater, Manager of Lifecycle Email Marketing at Litmus, puts it:
"It’s all about consistency. Spammers don’t have a regular cadence. They just randomly send emails, and a lot of them, all at once. If I send 1,000 emails, but I only send them randomly, it doesn’t look as good as 10,000 emails sent every month at the same time." [11]
In other words, it’s better to send emails consistently – even in smaller volumes – than to blast out large, random batches. For cold outreach, keep your daily volume low (20–30 emails for new domains, up to 100 per mailbox) to avoid triggering spam filters.
When it comes to cold email campaigns, pacing is key. Research shows that a structured approach – one initial email followed by two spaced-out follow-ups – can significantly improve reply rates. For example, sending the first follow-up three days after the initial email and the second follow-up six to seven days later can boost reply rates by nearly 50%. Campaigns using this three-email strategy see reply rates of 9.2% [12].
Authentication protocols like SPF, DKIM, and DMARC also play a role in building trust with ISPs. When paired with consistent sending practices, they help ensure your emails are recognized as legitimate and not flagged as spam.
Handling Complaints and Bounces
High complaint and bounce rates are red flags for ISPs and can seriously harm your sender reputation. To stay in the clear, keep your complaint rate below 0.3% – this means fewer than 3 spam complaints for every 1,000 emails sent.
Address complaints and bounces quickly. Hard bounces (invalid addresses) should be removed immediately, as continuing to send to these addresses signals poor list management. Soft bounces, on the other hand, require monitoring. If an address repeatedly soft bounces, it may indicate an inactive account that should also be removed.
Unsubscribe rates can offer valuable insights into your email strategy. For example, 44% of recipients unsubscribe because they feel overwhelmed by too many emails [12]. High unsubscribe rates often precede an increase in spam complaints, so optimizing your send frequency is crucial.
Set frequency limits within your marketing automation platform to prevent over-emailing. This ensures no single recipient feels bombarded, reducing the risk of complaints and unsubscribes.
The Bigger Picture
These factors don’t operate in isolation – they’re interconnected. Poor list hygiene can lead to higher complaint and bounce rates, which hurt your sender reputation and reduce inbox placement. In fact, only 83.1% of emails actually make it to the inbox, meaning nearly 1 in 6 gets filtered out before it’s even opened [12]. By managing these elements effectively, you can significantly improve your chances of reaching your audience and keeping them engaged.
Tools for Better Engagement and Deliverability
When it comes to email marketing, engagement is a key factor in ensuring your messages actually reach their intended audience. Specialized tools are crucial for providing the actionable insights needed to navigate the complexities of ISP filtering algorithms and monitor performance across various email providers. Relying on manual monitoring often means critical issues are identified too late. This is where tools like MailMonitor come into play, offering a modern, data-driven approach to improving email deliverability.
How MailMonitor Tracks Engagement
Tackling deliverability challenges requires precise, real-time tracking, and MailMonitor excels in this area. By using a network of over 400 seed accounts spread across 60+ ISPs, the platform provides detailed insights into where your emails land – whether it’s the inbox, spam folder, or promotions tab [15].
MailMonitor continuously monitors engagement signals and other critical reputation factors like email blocklists, spam traps, ISP behavior trends, and feedback from providers such as Microsoft SNDS and Google Postmaster Tools. Drawing from billions of inbox delivery events, the platform delivers tailored recommendations to help marketers pinpoint issues, whether they stem from authentication errors, reputation dips, or declining engagement levels.
Dan Westenskow, CEO of Fusion HCS, highlights the platform’s impact:
MailMonitor’s analytics gave us insight into which internal tools and practices were getting the best results. This allowed us to transition our entire salesforce from ineffective tools to more effective sending strategies. [16]
MailMonitor Features for Email Optimization
MailMonitor offers a suite of features designed to enhance email deliverability. It checks email authentication protocols like SPF, DKIM, and DMARC to ensure proper setup and alignment – key factors ISPs rely on to verify email legitimacy.
The platform also monitors infrastructure, detecting DNS and authentication issues early on, and provides tools for accurate email list verification to remove invalid addresses. It even identifies ISP throttling, helping marketers address potential bottlenecks.
Additional features include custom alerts for real-time notifications about deliverability risks and an email rendering preview that shows how messages appear across various devices and browsers. For businesses seeking deeper integration, MailMonitor offers API access and white-labeling options, along with managed services that include audits, remediation plans, and ongoing optimization support.
Benefits of MailMonitor for Email Marketers
The results speak for themselves. Fusion HCS saw a 90% boost in inbox placement across 1 million contacts using MailMonitor, while hubXChange saved $271,000 by resolving their email deliverability challenges [14]. These figures highlight the tangible impact of improved email performance.
MailMonitor’s approach focuses on breaking the engagement-reputation cycle that often determines email success. By providing clear visibility into how ISPs handle your emails, the platform transforms complex deliverability data into easy-to-understand, actionable insights.
Nathan Merryfield, Director of Marketing at hubXChange, shares his experience:
MailMonitor’s software is easy enough to understand for a beginner with little knowledge of email placement. But what sets them apart is their hands-on support to maximize our deliverability. The team is always friendly and responsive, even with challenging clients like us! [14]
With an overall rating of 5.0/5 based on 20 verified user reviews [13], MailMonitor is praised for its user-friendly interface, affordable seed testing, and proactive approach to identifying and resolving spam issues. For email marketers navigating the complexities of ISP filtering and engagement metrics, MailMonitor provides the tools and expert support needed to maintain a strong sender reputation and maximize inbox placement.
Key Takeaways
How Engagement-Based Filtering Works
Internet Service Providers (ISPs) no longer rely solely on analyzing email content to decide where your messages land. Instead, they now focus heavily on how recipients interact with your emails. This shift means your sender reputation is increasingly tied to user engagement. One of the most important metrics here is the engagement rate, which measures the ratio of positive actions (like opens and clicks) to the total number of emails delivered [19].
Positive interactions – such as opens, clicks, replies, and forwards – help improve your chances of landing in the inbox. On the other hand, negative signals like spam complaints, unsubscribes, or non-engagement can push your emails straight into the spam folder [19][20].
Your sender reputation remains crucial for deliverability. Factors like engagement rates, keeping spam complaints under 0.1%, low bounce rates, and proper authentication protocols all play a role [19]. Be cautious of sudden spikes in email volume or sending to inactive users, as these can quickly harm your reputation.
ISPs are also getting smarter at spotting bot activity. By analyzing patterns such as IP addresses, user agents, and the timing or frequency of clicks, they can differentiate real user engagement from automated actions [17]. For instance, a flurry of clicks immediately after opening an email often signals bot activity rather than genuine interest [17].
These insights are key to making meaningful changes that improve your email performance.
Next Steps for Email Marketers
To maintain strong inbox placement, focus on strategies that prioritize engagement. Start by auditing your metrics and systematically improving them. Regularly clean your email lists to remove inactive or unengaged contacts – this reduces bounce rates and complaints while improving overall engagement [18].
Pay special attention to your most engaged users, especially when warming up a new IP or launching a campaign. ISPs reward consistent, positive engagement patterns [19]. Also, ensure your emails are secured with proper authentication protocols like SPF, DKIM, and DMARC. These build trust with ISPs and help protect your sender reputation [19][17].
Personalize your content to make it more relevant to your audience. Craft compelling subject lines to drive opens and clicks, and segment your lists based on user engagement history to tailor your messaging. Regular testing with specialized tools can help you identify and address potential deliverability issues before they escalate.
For deeper insights, consider working with deliverability experts or using platforms like MailMonitor to track your inbox placement, engagement metrics, and sender reputation. Staying on top of ISP filtering trends and continuously fine-tuning your approach will help you stay ahead.
Finally, always prioritize explicit permission and invest in building long-term relationships with your audience. This not only fosters trust but also strengthens your sender reputation over time.
FAQs
How can I boost my sender reputation to improve email deliverability?
To improve your sender reputation and make sure your emails actually land in inboxes, start by setting up SPF, DKIM, and DMARC protocols. These authentication methods verify that your emails are legitimate and not spoofed. Another key step is to regularly clean your email list – remove invalid addresses and inactive subscribers. This helps cut down on bounces and reduces the risk of spam complaints.
If you’re working with a new sending domain or IP, use IP warming to gradually increase your email volume over time. Stick to consistent sending practices, steer clear of spammy language, and avoid buying email lists at all costs. To stay on track, use monitoring tools to keep an eye on your sender reputation and analyze your email performance.
By following these practices, you can build credibility with ISPs and increase the likelihood of your emails landing in your audience’s inbox.
How can you tell the difference between real user engagement and bot activity in email marketing?
To distinguish genuine user engagement from bot activity in email marketing, take a closer look at interaction patterns. Bots tend to click on links almost instantly after an email is delivered, while real users display more natural behaviors, like delayed clicks or interacting selectively with certain links.
Another effective approach is segmenting your audience based on their engagement levels. This can help spot unusual patterns that might suggest automated activity. By doing this, you ensure your metrics represent actual user behavior, which is crucial for maintaining accurate deliverability insights.
What role do SPF, DKIM, and DMARC play in improving email deliverability and protecting sender reputation?
SPF, DKIM, and DMARC are key email authentication tools designed to verify that an email truly comes from the sender’s domain. SPF (Sender Policy Framework) ensures that only approved servers can send emails on behalf of your domain. DKIM (DomainKeys Identified Mail) attaches a digital signature to your emails, confirming they haven’t been tampered with during transit. Finally, DMARC (Domain-based Message Authentication, Reporting, and Conformance) ties these protocols together, enforcing your domain’s policies and helping to prevent email spoofing.
When businesses use these protocols, they can enhance email deliverability, avoid having their messages flagged as spam, and protect their domain’s reputation. Together, SPF, DKIM, and DMARC create a safer email-sending process, ensuring your emails land in the right inboxes.
