What are Sender Score's Sending IPs and how to troubleshoot sudden email open rate declines?
Matthew Whittaker
Co-founder & CTO, Suped
Published 8 Jun 2025
Updated 19 Aug 2025
9 min read
Understanding what Sender Score's sending IPs are and why your email open rates might suddenly decline is crucial for maintaining effective email campaigns. Email deliverability is a complex landscape, and a sudden drop in engagement metrics, like open rates, can be a frustrating and perplexing issue for any sender. It often signals underlying problems with your sender reputation, which is heavily influenced by the IP addresses used to send your emails.
This guide will clarify what these sending IPs represent, explain how they relate to your Sender Score, and provide actionable steps to troubleshoot and recover from an unexpected decrease in your email open rates. We'll delve into various factors that can impact your deliverability, from technical configurations to content and audience engagement, helping you pinpoint the root cause and implement effective solutions.
What are sender score's sending IPs?
Sender Score is a reputation metric provided by Validity, designed to assess the trustworthiness of an outgoing mail server's IP address. It assigns a rating from 0 to 100, where a higher score indicates a better reputation and a greater likelihood of your emails reaching the inbox rather than the spam folder. Think of it like a credit score for your email sending infrastructure.
The sending IPs that appear in your Sender Score report are the specific IP addresses from which your email campaigns are originating. For many senders, especially those using email service providers (ESPs), these might be shared IP addresses, meaning multiple senders use the same IP. For larger senders, they might be dedicated IPs exclusively used by their domain. The reputation of these IPs directly influences how internet service providers (ISPs) like Google and Outlook perceive your email.
Sometimes, you might see unexpected IP addresses in your Sender Score report. This can happen if you are using a relaying or forwarding service. If your mailbox provider (Provider A) forwards emails to another provider (Provider B), the IP address associated with Provider A might show up in your report, even if you don't directly manage it. This is typically not a cause for concern unless that specific IP has a consistently low score or is associated with spam activity outside your control. Understanding why unexpected IP addresses appear is the first step in making sense of your reputation data.
Why open rates suddenly decline
A sudden decline in email open rates can be alarming and points to a potential issue with your email deliverability or how your audience perceives your messages. While a dropping Sender Score on your sending IPs can certainly contribute, it's often part of a larger picture. Many factors influence whether your email lands in the inbox or the spam folder, and whether recipients actually open it.
One significant factor is sender reputation, which encompasses both your IP and domain reputation. Mailbox providers assess this based on various engagement metrics, including spam complaints, bounce rates, and whether recipients open or delete your emails without opening. A poor reputation can lead to emails being filtered directly to spam, impacting your open rates even if they technically "delivered." You can find more information about this at Mailforge's article on sender reputation factors.
Beyond reputation, issues with your email list hygiene, content relevance, and even sending frequency can lead to declining open rates. Sending to disengaged subscribers, using generic subject lines, or having inconsistent sending volumes can all signal to ISPs that your emails are less desirable, leading to poorer inbox placement. It's essential to look at the broader context of your email program, not just isolated metrics.
Troubleshooting sudden open rate declines
When facing a sudden drop in open rates, a systematic troubleshooting approach is necessary. Start by checking your email service provider's dashboards for any anomalies. Look for increases in bounce rates, particularly hard bounces, which indicate invalid addresses. An uptick in spam complaints is a critical red flag, as ISPs heavily weigh this metric when determining reputation. You should also compare your current performance against historical data and industry benchmarks to identify the exact timeframe and magnitude of the drop. For instance, a small dip might be normal fluctuation, but a significant decline of 10% or more warrants immediate investigation.
Next, evaluate your audience engagement and email content. Have you recently changed your subject lines or preheader text? Are you segmenting your audience effectively? A lack of personalization or irrelevant content can lead to lower opens, even if emails reach the inbox. Consider performing an email deliverability test to see where your emails are landing across different mailbox providers. This can reveal if the issue is widespread or specific to certain providers like Hotmail or Yahoo Mail, suggesting a potential IP or domain blocklist (or blacklist) issue.
After identifying the potential causes, it's time to implement strategies to improve your open rates and overall deliverability. One of the most important aspects is maintaining a clean and engaged email list. Regularly remove inactive subscribers and hard bounces. Sending to unengaged addresses can significantly hurt your sender reputation and lead to lower open rates, even increasing spam complaints over time. Implement a re-engagement strategy for inactive subscribers or remove them if they don't respond.
Focus on email authentication by ensuring your SPF, DKIM, and DMARC records are correctly configured. These protocols help mailbox providers verify that your emails are legitimate and prevent spoofing. A proper setup improves your perceived trustworthiness and can prevent your emails from being flagged as suspicious. Also, maintain a consistent sending volume and frequency. Sudden spikes or drops in email volume can trigger spam filters and negatively impact your IP reputation (or blacklist status).
Continuously monitor your blocklist (or blacklist) status for both your sending IPs and domain. Being listed on a major blocklist can severely hinder deliverability. If you find yourself on a blocklist, act quickly to understand the reason and request delisting. Remember, improving email deliverability and open rates is an ongoing process that requires constant monitoring and adaptation to maintain a strong sender reputation and ensure your messages reach your audience effectively.
Troubleshooting actions and best practices
Causes of declined open rates
Reputation issues: Poor sender reputation, potentially due to high spam complaints or bounces, can lead to emails going to spam.
IP/domain blocklisting: If your sending IP or domain is on a blocklist (or blacklist), emails may be rejected or heavily filtered.
Authentication failures: Incorrect SPF, DKIM, or DMARC setup can cause emails to fail authentication checks.
Check ISP feedback loops: Utilize Google Postmaster Tools and Microsoft SNDS for reputation data.
Verify authentication: Confirm SPF, DKIM, and DMARC are correctly set up and aligned.
Review content and list hygiene: Ensure content is relevant and lists are regularly cleaned for inactive subscribers and spam traps.
Understanding the interplay of factors
Impact of IP reputation
Your email's journey to the inbox heavily depends on the reputation of the sending IP address. A strong IP reputation means ISPs trust your sending practices, leading to better deliverability and higher open rates. Conversely, a poor IP reputation can result in emails being blocked or routed to the spam folder. This is particularly true if your IP (or domain) ends up on an email blacklist (or blocklist). Maintaining a positive IP reputation involves consistent, legitimate sending behavior and adherence to best practices, as highlighted by Mailpro's guide on IP reputation.
Impact of content and audience
Even with a stellar IP reputation, your email content and audience engagement significantly influence open rates. Irrelevant content, generic subject lines, or poor calls to action can lead recipients to ignore your emails, or worse, mark them as spam. A high volume of unopens signals to ISPs that your content is not valuable, affecting your future deliverability. Engaging your audience with personalized, relevant content, and maintaining a clean, active email list are just as vital as your IP reputation. A balanced approach considering both technical aspects and audience engagement is key to maximizing open rates.
Effective email deliverability extends beyond just IP reputation; it involves a holistic approach to your entire email program. This includes consistent list hygiene, robust email authentication protocols like SPF, DKIM, and DMARC, and meticulous content creation to ensure relevance and engagement. Your overall domain reputation also plays a crucial role. For a deeper understanding of these concepts and how they contribute to your email health, exploring resources on how to diagnose sudden drops in email open rates is essential.
When you notice a drop in your Sender Score, investigate not only the IPs but also recent changes in your sending behavior. Did you acquire a new list? Change ESPs? Or alter your email content significantly? Any of these could contribute to a shift in how ISPs perceive your email. Remember, every email you send builds (or erodes) your reputation, making consistent adherence to best practices paramount. This ongoing effort is vital for boosting email deliverability rates and improving your overall sender score.
Views from the trenches
Best practices
Actively monitor your IP and domain reputation using tools like Google Postmaster and Microsoft SNDS.
Segment your audience and personalize content to increase engagement and reduce spam complaints.
Implement robust email authentication (SPF, DKIM, DMARC) for all sending domains.
Maintain a consistent email sending volume to avoid triggering suspicious activity alerts.
Regularly clean your email lists by removing inactive subscribers and hard bounces.
Common pitfalls
Ignoring sudden drops in open rates, attributing them to external factors without investigation.
Sending to unengaged or old email lists, which can increase spam complaints and bounces.
Failing to monitor your IP and domain for blocklistings or blacklists.
Inconsistent sending patterns, such as sudden high volumes from a previously low-volume IP.
Neglecting email authentication, making your emails appear untrustworthy to ISPs.
Expert tips
A sudden drop in open rates often indicates a deliverability issue, possibly related to IP reputation or blocklist status.
Review your sending practices for any recent changes that could impact deliverability.
Utilize ISP-specific tools like Google Postmaster and Microsoft SNDS for detailed reputation insights.
Ensure your email authentication records (SPF, DKIM, DMARC) are correctly configured.
A marketer from Email Geeks says that sometimes the sending IP in Sender Score can be a relaying or forwarding service, and if one mailbox provider forwards emails to another, the IP of the first provider might show up.
2019-11-07 - Email Geeks
Expert view
An expert from Email Geeks explains that Sender Score lists the IP addresses sending on behalf of your domain, and their reputation is based on the quality of emails detected by their sensors.
2019-11-07 - Email Geeks
Final thoughts on email deliverability
Understanding Sender Score's sending IPs and proactively troubleshooting sudden open rate declines are essential components of a robust email deliverability strategy. It's not enough to simply send emails; you must ensure they consistently reach the inbox and engage your audience. By actively monitoring your reputation metrics, addressing technical configurations, and refining your content strategy, you can mitigate potential issues and maintain strong email performance.
Remember that email deliverability is a dynamic field, and what works today might need adjustment tomorrow. Continuous learning and vigilance are key to navigating its complexities. By taking a proactive approach to your sender reputation and addressing any dips in open rates swiftly, you ensure your valuable messages consistently reach their intended recipients, fostering engagement and driving successful outcomes for your email campaigns.
Google and 
Outlook perceive your email.
Hotmail or 
Yahoo Mail, suggesting a potential IP or domain blocklist (or blacklist) issue.
Google Postmaster Tools for your sending domain and 
Microsoft SNDS for your sending IP addresses. These free tools offer invaluable insights into your sender reputation, complaint rates, IP reputation, and DMARC failures, which are crucial for understanding drops in Gmail open rates or sudden open rate drops for a large newsletter. If you notice SenderScore showing inaccurate data or low scores that don't align with your perceived sending practices, these tools can provide a more granular view.
