How to test email deliverability using seedlists and DMARC configurations?
Matthew Whittaker
Co-founder & CTO, Suped
Published 23 Jun 2025
Updated 19 Aug 2025
6 min read
Ensuring your emails reach their intended recipients is a continuous challenge for any sender. Email deliverability isn't just about sending emails, it's about landing them in the inbox, not the spam folder or, worse, being rejected entirely. Many factors influence whether an email makes it, from sender reputation to authentication protocols.
For years, I've seen businesses struggle with inconsistent inbox placement, leading to missed opportunities and frustrated audiences. Effective testing is the only way to gain clear insights into how mailbox providers (ISPs) view your sending practices and email content.
Two of the most powerful and complementary methods for diagnosing and improving email deliverability are using seedlists and properly configuring DMARC. Both provide distinct yet equally vital perspectives on your email program's health, helping you identify issues before they impact your audience.
Seedlist testing involves sending your email campaigns to a curated list of email addresses across various internet service providers (ISPs) and different mailbox types. This gives you a real-world snapshot of where your email lands, whether it's the inbox, spam folder, or if it's blocked.
The core idea is to replicate your subscribers' experience. By observing how these test addresses receive your emails, you can pinpoint potential problems with content, sending reputation, or authentication. Regular seedlist testing helps improve email deliverability by giving you insights into how you're inboxing. You can gain valuable insights by testing your deliverability this way.
There are different approaches to seedlist testing, from manual observation to using automated tools. Automated tools often provide more granular data and cover a wider range of ISPs, including major players like Gmail and Yahoo. I highly recommend using a comprehensive email deliverability tester to get a clear picture of your inbox placement.
Manual seedlist testing
Setup: Create a small list of email addresses across different providers like Gmail, Yahoo, and Outlook, ensuring you have access to each inbox.
Execution: Include these addresses in your regular email send and manually check where each email lands (inbox, spam, promotions, etc.).
Limitations: Time-consuming, limited ISP coverage, and difficult to scale or analyze trends over time.
Leveraging DMARC for deliverability insights
DMARC (Domain-based Message Authentication, Reporting, and Conformance) is another critical component of email deliverability testing. It builds upon SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) to provide robust email authentication, ensuring that emails purporting to be from your domain are legitimate. DMARC configurations are needed for email security.
One of the most valuable aspects of DMARC is its reporting capability. When you implement a DMARC record, ISPs that receive emails from your domain will send you XML reports (RUA reports) detailing authentication results. These reports offer a comprehensive overview of your email traffic, showing which emails passed DMARC, SPF, and DKIM, and which failed. You can see how to verify DMARC, DKIM, and SPF setup.
Analyzing DMARC reports allows you to identify unauthorized senders spoofing your domain, misconfigured authentication records, or legitimate sending sources that aren't properly authenticated. This data is crucial for protecting your brand from phishing and ensuring your legitimate emails reach the inbox. Understanding and troubleshooting DMARC reports from Google and Yahoo is key.
DMARC policies for testing
p=none: This policy instructs receiving mail servers to take no action on emails that fail DMARC, but still send reports. It's ideal for initial deployment and monitoring without impacting deliverability.
p=quarantine: Emails failing DMARC will be treated with suspicion, often sent to the spam or junk folder. This is a good intermediate step to test the impact before full enforcement.
p=reject: Emails failing DMARC will be rejected outright, meaning they won't even reach the recipient's spam folder. This is the strongest policy, offering maximum protection against spoofing but requiring careful monitoring.
Combining seedlists and DMARC for comprehensive testing
While seedlists and DMARC serve different purposes, they are most effective when used together. Seedlists provide a practical view of where your emails land, showing you the end result of your sending efforts. DMARC, on the other hand, gives you the underlying technical data about why those emails might be landing in a particular place, especially concerning authentication.
For example, if your seedlist test shows emails landing in the spam folder at Gmail, your DMARC reports can help diagnose if it's due to an SPF alignment failure or a DKIM signature issue. Without DMARC data, you might be left guessing the technical root cause. This combination helps to accurately test and measure email deliverability and sender reputation.
Conversely, even with perfect DMARC alignment, emails can still go to spam if your content triggers filters or your sender reputation is poor. Seedlists catch these issues. Together, they provide a holistic view, allowing you to fine-tune both your technical setup and your email content strategy. This comprehensive approach is essential for anyone aiming to improve email deliverability consistently.
Inbox placement (seedlists)
Direct view: See exactly where emails land (inbox, spam, promotions, missing).
Content impact: Helps identify issues related to email content, subject lines, or spam triggers.
Sender reputation: Provides insights into how your sender reputation affects different ISPs.
Authentication issues (DMARC)
Technical diagnosis: Pinpoints failures in SPF, DKIM, or DMARC alignment.
Spoofing detection: Identifies unauthorized entities sending emails on behalf of your domain.
Policy enforcement: Allows you to move towards stricter policies (quarantine, reject) with confidence.
Best practices for consistent deliverability testing
To maintain optimal email deliverability, testing shouldn't be a one-time event. It needs to be an ongoing process. Regular, consistent testing allows you to detect subtle shifts in ISP behavior, changes in your sender reputation, or new issues that might arise from content updates or infrastructure changes.
Schedule regular seedlist tests, ideally before every major campaign or on a weekly basis for ongoing programs. Similarly, review your DMARC reports daily or weekly, paying close attention to aggregate data and forensic reports if available. Early detection of issues can prevent significant drops in inbox placement and protect your domain reputation. You might want to get started with our email deliverability test checklist.
Don't forget to also monitor major blocklists (also known as blacklists). While DMARC helps with authentication failures and spoofing, getting listed on a blocklist can severely impact your deliverability, regardless of your DMARC configuration. Incorporating blocklist monitoring into your routine provides another layer of protection. Checking your email domain reputation regularly can also prevent unexpected deliverability drops.
Views from the trenches
Best practices
Always get a baseline of your current deliverability before making any changes to your sending infrastructure or authentication setup. This helps in understanding the impact of your optimizations.
Integrate seedlist testing into your pre-send checklist for every major campaign. This catches content-related issues or sudden reputation drops before they affect your entire list.
Actively monitor DMARC aggregate reports (RUA). These reports are goldmines for identifying legitimate and unauthorized sending sources that impact your deliverability.
When troubleshooting, compare seedlist results with DMARC reports. Inbox placement issues could be due to authentication failures highlighted in DMARC.
Start with DMARC's 'p=none' policy to gather data without impacting email delivery, then gradually move to 'quarantine' or 'reject' as you gain confidence.
Common pitfalls
Relying solely on DMARC without checking actual inbox placement, as DMARC only covers authentication, not content or reputation filters.
Ignoring DMARC reports or not setting up proper reporting channels, missing critical insights into spoofing attempts or misconfigurations.
Using a seedlist that's too small or doesn't include a diverse range of ISPs and mailbox types, leading to an incomplete picture of deliverability.
Not regularly updating or diversifying your seedlist, which can lead to stale data that doesn't reflect current ISP filtering trends.
Failing to address blocklist (or blacklist) listings in conjunction with DMARC and seedlist results, as blocklistings can override good authentication.
Expert tips
For cold email campaigns, use business email addresses for seedlist testing, not personal ones, to get more accurate deliverability results.
When using an ESP for testing, ensure your domain is correctly set as the 'Sender FROM' to accurately test your domain's authentication.
Automated seedlist tools often provide detailed insights into bounces and errors beyond just inbox placement, which is crucial for in-depth analysis.
Don't just look at a single number for deliverability; analyze the granular details provided by seedlist and DMARC tools, especially for major ISPs.
Consider how DMARC policies like 'p=reject' for your organizational domain affect deliverability when an ESP sends emails on your behalf.
Marketer view
Marketer from Email Geeks says they use seedlists from tools that cover a wide range of email addresses, including Gmail, Yahoo, Hotmail, and business domains, to get a comprehensive view of inbox placement.
2023-01-19 - Email Geeks
Marketer view
Marketer from Email Geeks says it's important to get real bounce and error reports from seedlist testing, not just a numerical score, to understand the specific issues affecting deliverability.
2023-01-20 - Email Geeks
Final thoughts on testing
Testing email deliverability using seedlists and DMARC configurations is not merely a technical exercise, it's a fundamental practice for any sender aiming to achieve consistent inbox placement and protect their brand. Seedlists provide a direct view into where your emails land, while DMARC offers the technical insights into your email authentication health.
By combining these two powerful methods, you gain a comprehensive understanding of your email program's strengths and weaknesses. This allows for proactive troubleshooting, preventing deliverability issues before they escalate and impact your audience engagement and campaign ROI.
Regular testing and diligent analysis of the data provided by both seedlists and DMARC reports are paramount. This iterative process of testing, analyzing, and optimizing will ensure your emails consistently reach the inbox, fostering stronger connections with your subscribers and protecting your sending reputation.
Yahoo. I highly recommend using a comprehensive email deliverability tester to get a clear picture of your inbox placement.
Gmail, your DMARC reports can help diagnose if it's due to an SPF alignment failure or a DKIM signature issue. Without DMARC data, you might be left guessing the technical root cause. This combination helps to accurately test and measure email deliverability and sender reputation.
