How does Google Postmaster Tools IP reputation affect deliverability when open rates are stable?
Michael Ko
Co-founder & CEO, Suped
Published 30 Jun 2025
Updated 30 Sep 2025
8 min read
It's easy to look at your email open rates and assume everything is fine, especially when they remain consistent. However, a declining Google Postmaster Tools (GPT) IP reputation can be a silent alarm, signaling underlying deliverability issues that haven't yet manifested in your top-line metrics. Many email senders face this dilemma, seeing their IP reputation in GPT shift from green to yellow or even red, yet their reported open rates stay the same. This can lead to a false sense of security within marketing teams.
The critical point to understand is that open rates, while important, are often a lagging indicator. They reflect what has already happened, not necessarily what is currently happening with your inbox placement, especially when dealing with the nuanced filtering algorithms of major inbox providers like Gmail. An email can still be opened even if it lands in the spam folder, particularly by highly engaged users who actively seek out your messages.
This situation highlights a common pitfall in email deliverability monitoring. Relying solely on open rates can obscure more insidious problems that are brewing beneath the surface. Ignoring a poor IP reputation in Google Postmaster Tools can lead to a gradual but significant decline in email deliverability over time, affecting new subscribers or less engaged segments first. Understanding the relationship between IP reputation, domain reputation, and overall sender health is key to maintaining optimal inbox placement.
The nuanced relationship between IP and domain reputation
IP reputation and domain reputation are both crucial, yet distinct, components of your sender score. While they are often intertwined, they can sometimes tell different stories. Your domain reputation reflects the sending behavior associated with your brand and domain name, which is more portable and long-lived, following you even if you change email services or IP addresses. Conversely, IP reputation is tied directly to the sending IP address and is highly sensitive to the volume and quality of mail sent from that specific IP.
In many cases, a strong domain reputation can somewhat buffer the immediate impact of a dipping IP reputation, especially for highly engaged recipients. This could explain why open rates initially remain stable. However, if the IP reputation continues to decline, it will inevitably start to drag down the domain reputation as well, leading to broader deliverability issues across all mailbox providers. It is important to monitor both metrics closely.
IP reputation factors
Sending volume stability: Sudden spikes can trigger filters.
Spam complaints: High rates directly damage IP standing.
Blacklist (or blocklist) presence: Getting listed on a blocklist instantly harms IP reputation.
Content quality: Relevance and engagement of your messages.
Subscriber engagement: Opens, clicks, and replies from recipients.
Unsubscribe rates: High rates signal subscriber dissatisfaction.
For dedicated sending IPs, your IP reputation is solely your responsibility. Any issue directly reflects on your sending practices. For shared IPs, your reputation is linked to other senders using the same IP, which can be both a blessing and a curse. While it might cushion minor individual issues, a bad actor on a shared IP can negatively affect everyone else's deliverability. Google considers historical data for both, so consistent performance is key.
Why stable open rates can be misleading
When your Google Postmaster Tools IP reputation decreases but open rates remain stable, it's a sign that the negative impact hasn't fully cascaded through your metrics yet. Google's documentation clearly states that messages from senders with a low reputation have an increased likelihood of being filtered to the junk folder. This filtering can be subtle and doesn't always result in an immediate, drastic drop in open rates, especially for engaged subscribers.
One reason for this delayed effect is that some users might actively check their spam folder for your emails if they expect them, or if previous emails from your domain consistently landed in the inbox. Their continued opens, even from spam, can temporarily mask the underlying deliverability problem in your reporting. Additionally, the impact might be gradual, affecting less engaged segments of your audience first, or specific ISPs that are more sensitive to IP reputation.
Warning: Ignoring IP reputation can be costly
A persistent low IP reputation, even with stable open rates, is a ticking time bomb. It can lead to:
Gradual decline: Slow erosion of inbox placement, particularly for new or less active subscribers.
Brand damage: Your brand being associated with spam, leading to decreased trust.
Reduced campaign effectiveness: Even if opens are stable, your click-through rates and conversions may suffer if emails land in spam.
Domain reputation impact: Eventually, a poor IP reputation can negatively affect your domain reputation too.
It's imperative to look beyond surface-level metrics and use tools like Google Postmaster Tools to gain deeper insights into your sending health. A proactive approach to reputation management is far more effective than trying to recover after a significant drop in deliverability has already occurred.
Deciphering Google Postmaster Tools signals
When Google Postmaster Tools shows your IP reputation as yellow (medium) or red (low/bad), it means your emails are at an increased risk of being filtered into the spam folder for Gmail users. The exact percentage of emails hitting the spam folder versus the inbox isn't explicitly stated, but even a 'medium' reputation implies a higher probability of emails being flagged as junk.
Google provides general definitions for its reputation levels. For instance, a 'low' IP reputation means an increased likelihood of emails being filtered to spam or rejected. This directly impacts your deliverability, regardless of your open rates. To truly understand the extent of the problem, consider segmenting your open rate data specifically for Gmail users over time.
Example of a basic DMARC record to monitor delivery:DNS
Beyond Google Postmaster Tools, it is important to check other ISP-specific feedback loops and sender portals. For example, Microsoft's Sender Support Tools (SNDS) provides insights into your IP and domain health with Outlook.com users, which is essential as Hotmail (and its associated domains) are often very concerned with IP reputation.
A comprehensive approach to monitoring includes not just Google Postmaster Tools but also DMARC reporting, which gives a holistic view of email authentication and delivery. Tools like Suped's DMARC monitoring can consolidate these reports, making it easier to identify and address issues across all mailbox providers.
Strategies for improving IP reputation
If you notice a decline in your IP reputation, it's crucial to act promptly. Start by thoroughly reviewing your recent sending practices. Have there been any significant changes in list acquisition, email content, or sending volume? Consistent send volume is key, as large spikes can easily be flagged as suspicious, hurting your IP and domain reputation.
Another area to investigate is your spam complaint rates and unsubscribe rates. Even if open rates are stable, an increase in complaints or unsubscribes indicates that your audience is not happy with your emails, which directly impacts your reputation. High complaint rates are a major red flag for mailbox providers and will quickly push your emails to the spam folder or even lead to blocklisting (blacklisting).
Clean your email lists: Regularly remove inactive subscribers and hard bounces. Consider suppressing inactive segments for a period.
Segment your audience: Send targeted content to engaged users to maintain relevance and reduce complaints.
Monitor blocklists (blacklists): Utilize blocklist monitoring services to detect if your IP or domain is listed.
Review content for spam triggers: Avoid excessive capitalization, exclamation marks, or suspicious phrasing.
For shared IPs, work with your Email Service Provider (ESP) to understand their practices and ensure they are maintaining a healthy sending environment. For dedicated IPs, it's even more critical to manage your sending reputation meticulously. Consistent high volume, typically 50,000+ monthly emails, is often required to maintain a warm reputation on dedicated IPs.
Views from the trenches
Best practices
Monitor per-ISP open rates to identify specific providers where deliverability might be an issue despite overall stable metrics.
Segment your email lists into recently active and less engaged users to suppress inactive contacts for a period.
Actively track unsubscribe rates and spam complaints, as these are direct indicators of audience sentiment and reputation impact.
Implement strong email authentication, including DMARC, SPF, and DKIM, to protect your domain and improve trust.
Common pitfalls
Over-reliance on aggregate open rates, which can mask deliverability issues when emails land in spam but are still opened.
Ignoring Google Postmaster Tools' yellow or red IP reputation warnings, assuming stable open rates mean no problem.
Failing to check ISP-specific sender tools like Microsoft SNDS for a complete picture of deliverability.
Making large, sudden changes to email sending volume, which can trigger spam filters and damage IP reputation.
Expert tips
Domain reputation can sometimes be a more stable indicator than IP reputation, but both are crucial for holistic deliverability.
Consider that open rates can remain consistent even if emails land in spam, especially if users are actively looking for them.
Proactively segmenting your list and suppressing inactive users can help improve overall sender health and reputation.
Dedicated IPs require consistent high volume to maintain warmth, while shared IPs link your reputation to others.
Expert view
Expert from Email Geeks says that Google provides definitions indicating that low IP reputation increases the likelihood of being filtered to the junk folder, which directly impacts deliverability.
2019-12-21 - Email Geeks
Marketer view
Marketer from Email Geeks says that while domain reputation can be more important than IP reputation, it is actually a mix of both that determines delivery.
2019-12-21 - Email Geeks
Prioritizing your sender health
Ultimately, a stable open rate alongside a declining Google Postmaster Tools IP reputation is a clear indicator that deliverability problems are present or imminent. It's a call to action to investigate deeper than just your primary engagement metrics. Proactive monitoring, understanding the interplay of IP and domain reputation, and implementing best practices for list hygiene and sending consistency are vital.
By addressing these reputation issues head-on, you can prevent a subtle decline from turning into a major deliverability crisis, ensuring your emails consistently reach the inbox rather than being diverted to spam. Tools like Suped can provide the visibility needed to diagnose and resolve these complex deliverability challenges.
