How do tools like SNDS or Postmaster monitor IP health?
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Most deliverability tools give you a third-party view of your reputation. Google Postmaster Tools and Microsoft SNDS are different. They show you what the actual mailbox providers see. That distinction matters a lot when you're troubleshooting.
Mailbox providers built these tools because they wanted legitimate senders to have visibility and fix problems themselves, rather than flooding support queues with "why is my email going to spam" requests. The data comes directly from the provider's filters, not from a third-party proxy.
Google Postmaster Tools is domain-focused. You verify ownership of your sending domain and then see domain-level and IP-level reputation scores (high, medium, low, or bad), spam rates as a percentage of mail reaching Gmail, authentication pass rates for SPF, DKIM, and DMARC, and delivery errors with reason codes. The catch: you need to be sending at least a few hundred messages a day to Gmail before the data shows up. Below that threshold, it's mostly empty charts.
Microsoft SNDS (Smart Network Data Services) is IP-focused. You register the IPs you want to monitor, and it shows you a colour-coded reputation status (green, yellow, red) along with complaint rates and spam trap hits. The spam trap data is particularly useful because it can reveal list hygiene problems before they turn into blocklist listings. You can sign up for SNDS here.
Use both, not just one. Google Postmaster shows you domain reputation and authentication health. SNDS shows you IP-level signals and spam trap exposure. Neither covers everything the other does, and together they give you a complete picture of how the two biggest mailbox providers perceive your sending. If something's going wrong, one of these will usually show it before you start seeing widespread inbox placement problems.
One thing to watch: if your spam rate in Postmaster climbs above 0.1%, take it seriously right away. Google's own guidance says that's where deliverability starts to suffer. You can use our free Blocklist Checker alongside these tools to catch IP-level issues that might not surface in the provider dashboards yet.
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