How do ESPs track deliverability performance?

Your ESP dashboard is full of numbers. But which ones actually tell you if your deliverability is healthy, and which ones just look scary until you know the benchmarks?

Here's what ESPs track, what the numbers mean, and when you should actually worry.

Bounce rate is the first thing to watch. Hard bounces (permanent failures, like a non-existent address) should stay below 2%. If you're seeing more than that, your list needs attention. Soft bounces (temporary failures, like a full mailbox) are less alarming, but a spike there can signal a reputation problem. A good ESP will automatically suppress hard bounces so you don't keep hitting dead addresses.

Complaint rate is the one that keeps deliverability folks up at night. Gmail wants your complaint rate below 0.10%, and you'll start seeing serious problems above 0.30%. Yahoo Mail follows similar thresholds. Your ESP pulls these numbers from feedback loops that mailbox providers send back when someone hits "this is spam." If your complaint rate is creeping up, that's not a dashboard quirk. That's a signal to segment, re-permission, or cut your least engaged subscribers.

Delivery rate tells you what percentage of emails were accepted by the receiving server. Anything above 98% is generally healthy. But here's the catch: accepted doesn't mean inboxed. An email can be accepted and then sent straight to the spam folder. Delivery rate is a floor, not a ceiling.

Inbox placement rate is where it gets more interesting. Some ESPs (and third-party tools) test this using seed lists, sending to known test accounts across major providers to see where your emails land. You want to see 85% or above landing in the inbox. Below that, you've got a reputation problem worth diagnosing.

Engagement metrics (opens and clicks) are noisier than they used to be, especially after Apple's Mail Privacy Protection made open rates unreliable. But click-through rate still tells you something real. Low clicks combined with high complaints is a combination that accelerates reputation damage fast.

Beyond your dashboard, smarter ESPs also monitor things that happen at the infrastructure level. These include IP pool performance, authentication pass rates (SPF, DKIM, DMARC), and whether any of their sending IPs or domains have shown up on blocklists. You don't always see this layer directly, but it affects your deliverability. Platforms like Twilio SendGrid and Postmark expose more of this infrastructure data than average. Some ESPs also pull in data from Google Workspace Postmaster Tools if you've connected your domain, which gives you domain reputation and spam rate data straight from Google's side of the fence.

Here's a quick set of benchmarks to keep handy:

• Hard bounce rate: keep it below 2%
• Complaint rate: keep it below 0.10% (red flag above 0.30%)
• Delivery rate: aim for 98% or above
• Inbox placement rate: aim for 85% or above
• Authentication pass rate: SPF, DKIM, and DMARC should all be passing close to 100% of the time

If you're unsure whether your current setup is passing authentication correctly, our free SPF checker and DKIM lookup can tell you in seconds. Or if something is actively breaking, the SOS hotline is free to use.