What factors influence email deliverability and how does SenderScore work?
Matthew Whittaker
Co-founder & CTO, Suped
Published 29 May 2025
Updated 13 Oct 2025
7 min read
Email deliverability is far more complex than simply hitting 'send'. It's the art and science of ensuring your emails reach the intended inbox, rather than being diverted to spam folders or rejected entirely. Many intricate factors come into play, and understanding them is crucial for any email sender. One tool frequently mentioned in this context is SenderScore, which aims to provide a snapshot of your sending reputation. But how much weight should it truly hold, and what other elements are equally, if not more, important?
The success of your email campaigns, whether transactional or marketing, hinges on strong deliverability. It directly impacts engagement, conversions, and ultimately, your bottom line. Ignoring the various factors that influence it can lead to wasted effort and missed opportunities.
To effectively navigate the email landscape, it's essential to grasp how mailbox providers assess incoming mail and what metrics they prioritize. While tools like SenderScore offer valuable insights, they are just one piece of a much larger puzzle. Let's explore the critical components that collectively determine your email's fate.
Understanding email deliverability fundamentals
At the core of email deliverability lies sender reputation, which is a composite score assigned by Internet Service Providers (ISPs) and mailbox providers to an IP address or domain. A good reputation signals trustworthiness, while a poor one can lead to emails being blocked or sent to spam. This reputation is built over time based on numerous interactions and technical configurations.
Factors contributing to your sender reputation include your sending volume and consistency, the number of spam complaints you receive, and your bounce rates. ISPs analyze these metrics to decide whether your emails are legitimate or potentially unwanted. Maintaining a consistent sending pattern and keeping your email lists clean are vital for a positive reputation.
Email authentication protocols are also fundamental. SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting & Conformance) work together to verify that an email sender is authorized to send mail from a specific domain. Implementing these correctly is a non-negotiable step to prevent spoofing and improve trust with mailbox providers. Learn more about DMARC, SPF, and DKIM.
Core pillars of deliverability
Sender reputation: The overall trustworthiness of your sending IP and domain.
Email authentication: SPF, DKIM, and DMARC verify your identity and prevent spoofing.
Content quality: Relevant, engaging emails with proper formatting and no spammy triggers.
Recipient engagement: Opens, clicks, replies, and lack of complaints signal healthy mailing.
What is SenderScore and how it's calculated
SenderScore, provided by Return Path, is an email reputation metric that assesses an IP address's trustworthiness on a scale of 0 to 100. A higher score indicates a better reputation. This score is calculated using a proprietary algorithm that considers various factors, including spam complaints, blacklisting events, email volume, and infrastructure settings.
The data fueling SenderScore comes from a vast network of ISPs and email providers that share information about sending patterns. This aggregated data helps paint a picture of how an IP address behaves across the internet. It provides a useful benchmark for senders to understand where they stand in relation to others. You can check your score on SenderScore.org.
While a high SenderScore is generally a positive sign, it's important to remember it's one of many indicators. Some say a high score doesn't automatically guarantee inbox placement. Mailbox providers each have their own internal filtering algorithms, which may weigh different factors more heavily. For a deeper dive into how this score is determined, see how SenderScore impacts deliverability and its calculation.
SenderScore metrics
Spam complaints: High rates significantly lower your score.
Blocklists: Presence on major blocklists (or blacklists) heavily penalizes reputation.
Volume and consistency: Irregular or sudden spikes in volume can be suspicious.
Invalid recipients: High bounce rates suggest poor list hygiene.
Beyond the score
Engagement levels: Opens, clicks, and replies directly influence inbox placement.
Email authentication: Proper SPF, DKIM, and DMARC setup builds trust.
Content analysis: Spam filters scan for suspicious links, keywords, and formatting.
Subscriber list health: Quality over quantity helps avoid spam traps and bad addresses.
While SenderScore focuses on IP reputation, your overall deliverability is influenced by a broader array of factors. Crucially, user engagement metrics play a huge role. Mailbox providers closely monitor how recipients interact with your emails. High open rates, click-through rates, and replies signal that your emails are valued, leading to better inbox placement. Conversely, low engagement, high unsubscribe rates, or frequent spam complaints will quickly damage your standing.
Your email content itself is another significant factor. Spam filters are sophisticated and analyze everything from subject lines and body text to images and links. Avoid using spammy keywords, excessive capitalization, or broken HTML. Personalization and relevant content can significantly boost engagement and improve your deliverability. Additionally, maintaining a clean and segmented subscriber list ensures your messages are reaching interested recipients.
The health of your sending infrastructure is also paramount. This includes having proper DNS records, a dedicated IP address (if your volume warrants it), and ensuring your domain isn't associated with known spamming activities. Regularly monitoring your IP and domain for appearances on email blocklists (or blacklists) is a crucial preventative measure to safeguard your deliverability.
Improving your email deliverability requires a holistic approach, addressing both technical configurations and content strategy. Start by ensuring your email authentication protocols are correctly set up. Use a DMARC record generator if you don't have one, and monitor your DMARC reports closely with a tool like Suped, which offers the most generous free plan available for DMARC monitoring. This provides visibility into email authentication failures and potential threats.
Focus on building strong subscriber relationships. Segment your audience and send relevant, valuable content. Encourage engagement by asking recipients to add you to their address book or star your emails. Always provide a clear and easy unsubscribe option, as this can prevent spam complaints. If you're seeing a low SenderScore, dive into your engagement metrics and list health.
Regularly clean your email lists to remove inactive subscribers and invalid addresses, reducing bounce rates and the risk of hitting spam traps. Consider using a double opt-in process for new subscribers to ensure high-quality leads. For a deeper understanding of troubleshooting, refer to this guide on resolving email deliverability issues. Implementing these practices can significantly boost your inbox placement rates.
Neglecting authentication, leading to spoofing issues.
Segment your lists and personalize content.
Sending generic emails to entire, unsegmented lists.
Regularly clean email lists of inactive subscribers.
Maintaining outdated lists with high bounce rates.
Monitor your SenderScore and other reputation tools.
Ignoring reputation metrics until deliverability issues arise.
Views from the trenches
Best practices
Actively monitor your DMARC reports to catch authentication failures early.
Regularly segment your email lists to send targeted and relevant content.
Implement double opt-in for all new subscribers to maintain list quality.
Maintain consistent sending volumes to build a stable sender reputation.
Common pitfalls
Solely relying on SenderScore as the only indicator of deliverability health.
Ignoring email authentication protocols like SPF, DKIM, and DMARC.
Sending to unengaged subscribers, leading to high complaint rates.
Failing to monitor blocklists for your sending IPs and domains.
Expert tips
A comprehensive understanding of deliverability extends beyond just SenderScore.
Different mailbox providers weigh reputation factors differently.
Engagement signals (opens, clicks) are paramount to inbox placement.
Proactive list hygiene is essential to avoid spam traps.
Expert view
Expert from Email Geeks says: A high SenderScore is a helpful indicator, but it's not the only determinant for good deliverability.
2018-06-08 - Email Geeks
Marketer view
Marketer from Email Geeks says: We reviewed our client's ESP data, and their SenderScore was consistently in the high 90s, suggesting good reputation.
2018-06-08 - Email Geeks
Mastering the inbox journey
Achieving excellent email deliverability is an ongoing process that demands attention to detail across multiple fronts. While tools like SenderScore offer valuable insights into your IP reputation, they represent just one facet of the complex deliverability landscape. True success comes from a combination of robust technical setup, consistent sending practices, and a strong focus on subscriber engagement.
By prioritizing email authentication, maintaining clean lists, crafting engaging content, and continuously monitoring your performance, you can significantly improve your chances of reaching the inbox. Remember that every interaction, from a subscriber opening your email to a filter flagging it as spam, contributes to your overall sender reputation. With the right strategy and tools, you can ensure your messages land where they belong.
