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Deliverability isn't "set and forget." Sender reputation shifts constantly based on how people respond to your last several sends. Monitoring is how you catch a problem in week one instead of discovering it in week six, after revenue has already dropped.
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Most brands look at their "delivered" rate (95%+ is common) and assume everything's fine. That number just means the receiving server accepted the email — it says nothing about whether it landed in the primary inbox, promotions tab, or spam folder. Actual inbox placement across the industry averages only 83-85%. That gap is where revenue quietly disappears.
| Metric | Healthy benchmark | Action trigger |
|---|---|---|
| Spam complaint rate | Below 0.1% | Stop sending immediately, investigate before your next send — this is the single most damaging signal |
| Bounce rate | Below 2% | Run a list clean, check for a bad import or expired segment |
| Open rate (full list) | 20-30% average, 30%+ good | Below 20% on a full-list send signals a deliverability issue, not just a weak subject line |
| Unsubscribe rate | Below 0.3% per send | Review frequency and relevance/segmentation |
| Click rate | 2-3% average, 4%+ good (campaigns) | Low clicks despite decent opens = content/relevance problem, not deliverability |
The most important tool on this list. Shows your domain reputation (High/Medium/Low/Bad) directly from Gmail's perspective, plus spam rate, IP reputation, feedback loop data, and authentication success rate. Requires verifying your domain and adding a DNS TXT record. Check this weekly — it's the earliest warning system you have for Gmail deliverability specifically, and Gmail is where most ecommerce lists concentrate.
Send a test email to the address it generates, get a spam score out of 10 with a breakdown of exactly what's hurting you — authentication failures, content issues, blocklist hits, spam-trigger language. Run this before every major campaign and any time you change templates, sending domain, or platform.
Sends a test email to a panel of real seed addresses across Gmail, Outlook, Yahoo, and others, then reports exactly which folder it landed in per provider. This is the closest you can get to knowing your actual inbox placement rather than inferring it from open rates.