How reliable are GlockApps deliverability placement reports and what are the alternatives?
Matthew Whittaker
Co-founder & CTO, Suped
Published 2 May 2025
Updated 19 Aug 2025
7 min read
Email deliverability is a complex landscape, and understanding where your emails land is crucial for successful campaigns. Inbox placement reports, like those offered by GlockApps, aim to provide insight into whether your messages reach the inbox, spam folder, or are blocked entirely. These tools are designed to give senders a snapshot of how their emails are performing across various internet service providers (ISPs).
However, the reliability of these reports and their accuracy often come under scrutiny. Many email professionals question how truly representative these snapshots are of real-world performance. It's a critical discussion, as misinterpreting these reports can lead to unnecessary panic and misdirected efforts in optimizing your email program.
The role of inbox placement tests
Inbox placement tests typically work by sending your email to a seed list, which is a collection of email addresses across different domains and ESPs. The tool then tracks where the email lands for each seed address. This method provides quantitative data that can highlight potential deliverability issues before a large-scale send.
While useful for identifying foundational problems like authentication failures or immediate content-based spam triggers, these reports are often a snapshot and not a definitive declaration of your overall deliverability. They can certainly help you check if your emails are landing in the inbox or spam, or getting lost, as highlighted in some reviews. Many users have found them valuable for troubleshooting and fixing issues, particularly regarding blacklist (or blocklist) reports.
A common point of concern arises when a tool indicates an email is on numerous blocklists, yet a manual check using a comprehensive service like MultiRBL.valli.org shows no such listing. This discrepancy can indeed cause unnecessary alarm and divert resources to non-existent problems. The key is to understand the scope and limitations of the data provided.
Limitations of seed list data
The primary limitation of seed list data is that these accounts do not behave like real human subscribers. They do not open, click, reply, or mark emails as not spam. Modern inbox providers, especially those with advanced filtering algorithms like Gmail, heavily rely on subscriber-specific engagement patterns to determine inbox placement. A static seed list cannot replicate this dynamic behavior.
This leads to scenarios where a seed test might show poor placement, while your actual campaign metrics indicate strong engagement and inboxing. For instance, specific Outlook or Hotmail seed accounts in a test might show spam placement, but your real subscribers on those same domains are receiving emails in their primary inbox. This divergence stems from the lack of engagement history with seed accounts. Learn more about how reliable email deliverability data is from seed lists.
Another concern with these tools can be false positives, especially regarding blocklist reporting. Some tools may report a domain or IP as listed on a blocklist (or blacklist) that has little to no impact on actual deliverability, or one that is not widely used by major ESPs. This can create unwarranted stress and lead to unnecessary actions. Understanding how email blacklists actually work is essential.
Important caveat: seed list data
While seed list tests can be an initial diagnostic, they should not be the sole source of truth for your email deliverability. Always cross-reference their findings with real-world campaign performance data and direct feedback mechanisms from ISPs to avoid overreacting to potentially misleading results.
Leveraging real-world metrics and ESP feedback
For a more accurate understanding of your email deliverability, the most reliable data comes directly from your email service provider (ESP) and the engagement metrics of your actual subscribers. Key performance indicators (KPIs) like unique open rates, click-through rates, unsubscribe rates, and spam complaint rates provide a much clearer picture of how your emails are truly performing.
Furthermore, direct feedback tools from major ISPs are indispensable. Google Postmaster Tools (GPT) offer invaluable insights into your domain and IP reputation, spam rates, and authentication errors (SPF, DKIM, DMARC) directly from Google's perspective. Similarly, Microsoft offers similar services that provide direct feedback for Outlook/Hotmail domains. If these dashboards show high domain and IP reputation with low spam spikes, your deliverability is likely strong, regardless of what a seed test indicates.
The information provided by your internal KPI trends and Postmaster Tools is generally far more accurate and actionable than data from seed lists alone. These sources reflect the actual interaction of recipients with your emails, which is the ultimate determinant of deliverability. Focusing on these metrics helps you identify and address real deliverability issues, rather than chasing phantom problems.
Strategic use of testing tools
While seed testing tools like GlockApps have their limitations, they can still play a role in a comprehensive deliverability strategy, particularly as a preliminary diagnostic. They are effective for a quick health check of your email setup, especially for detecting immediate issues with authentication, content, or initial blacklist (or blocklist) presence. For a broader perspective on available options, you can explore email deliverability tools reviewed by industry experts.
A balanced approach involves integrating data from various sources. Use seed tests to identify glaring errors, then validate those findings with your internal analytics and, most importantly, Postmaster Tools data. For instance, if a seed test flags a blocklist issue, verify it with a reliable blocklist checker and check your DMARC reports for authentication alignment failures.
Ultimately, a proactive deliverability strategy hinges on continuous monitoring and a deep understanding of what truly influences inbox placement. While tools can offer insights, the most robust approach relies on direct ESP feedback, real engagement data, and sound email sending practices. For more on testing, see our guide on how to measure email deliverability and inbox placement rates.
Views from the trenches
Best practices
Always prioritize your own campaign KPIs: open rates, click-through rates, and complaint rates.
Regularly check Google Postmaster Tools and similar ISP dashboards for your domain and IP reputation.
Use blocklist checkers like MultiRBL.valli.org to verify any blocklist reports from testing tools.
Common pitfalls
Over-relying solely on seed list data, which does not reflect actual human engagement.
Panicking over blocklist reports from less impactful or obscure blocklists.
Ignoring real-world engagement metrics in favor of theoretical test results.
Expert tips
Seed tests can highlight immediate technical issues, but human behavior is the ultimate determinant.
If Postmaster Tools show good reputation and low spam, minor seed test anomalies are usually negligible.
Focus on the major ISPs like Gmail, Outlook, and Yahoo, as their filtering rules are the most impactful.
Marketer view
Marketer from Email Geeks says they feel GlockApps can cause unnecessary panic for clients, as its placement emails don't simulate actual human behavior, leading to potentially misleading results, especially for legacy Gmail accounts.
2024-06-20 - Email Geeks
Marketer view
Marketer from Email Geeks says that while seed list data can be useful, organic data and Postmaster Tools are always more accurate for assessing true deliverability.
2024-06-20 - Email Geeks
Moving beyond surface-level reports
While tools like GlockApps can be helpful for initial diagnostics and understanding specific technical configurations, their deliverability placement reports, especially those based solely on seed lists, should be viewed with a critical eye. The dynamic nature of email filtering, driven by personalized engagement algorithms, means that no static test can fully replicate real-world inbox placement.
For the most reliable insights, focus on your internal campaign metrics and the direct feedback provided by major ISPs through their Postmaster Tools. These sources offer the most accurate reflection of how your emails are performing for your actual subscribers. By combining these direct data points with strategic, informed use of testing tools, you can build a truly robust email deliverability program.
Gmail, heavily rely on subscriber-specific engagement patterns to determine inbox placement. A static seed list cannot replicate this dynamic behavior.
Outlook or 
Hotmail seed accounts in a test might show spam placement, but your real subscribers on those same domains are receiving emails in their primary inbox. This divergence stems from the lack of engagement history with seed accounts. Learn more about how reliable email deliverability data is from seed lists.
Google Postmaster Tools (GPT) offer invaluable insights into your domain and IP reputation, spam rates, and authentication errors (SPF, DKIM, DMARC) directly from Google's perspective. Similarly, 
Microsoft offers similar services that provide direct feedback for Outlook/Hotmail domains. If these dashboards show high domain and IP reputation with low spam spikes, your deliverability is likely strong, regardless of what a seed test indicates.
