Inbox placement rate (IPR) is the share of email you send that lands in the recipient’s primary inbox — not the spam folder, not the promotions tab, not filtered to a secondary category.
Why IPR matters more than uptime
Email vendors publish uptime figures (“99.9% uptime”) because uptime is easy to measure and makes them look good. IPR is hard to measure and makes most providers look mediocre.
A 99.9% uptime figure tells you the servers stayed on. It tells you nothing about whether the email you sent actually reached the person you sent it to.
Consider: a message can be successfully sent (uptime metric counts it as success) and simultaneously land in the recipient’s spam folder (IPR counts it as a miss). The message was delivered; it was just invisible.
How IPR is measured
IPR is measured using seed list testing: sending test messages from your domain to a controlled list of real inboxes at major providers (Gmail, Outlook, Yahoo, Apple Mail), then checking where each message lands.
In our Q1 2026 test, we seeded 200 messages per provider across 4 receiving services (Gmail, Outlook, Yahoo, Apple Mail) and recorded:
- Primary inbox landing
- Promotions/Other tab landing
- Spam folder landing
- Bounce
The IPR figure is the percentage landing in primary inbox.
What IPR scores mean in practice
| IPR | What it means |
|---|---|
| 85%+ | Excellent — strong domain reputation, minimal spam hits |
| 75-84% | Good — acceptable for most business use cases |
| 60-74% | Marginal — losses visible at modest send volume |
| Under 60% | Poor — significant deliverability risk |
From our Q1 2026 test:
- Google Workspace: 87% (excellent)
- Microsoft 365: 82% (good)
- Fastmail: 79% (good)
- Proton Mail: 76% (good)
- Zoho Mail: 71% (marginal for outbound-heavy senders)
- Hostinger: 43% (poor)
Why the gap between providers is structural
The IPR gap between Google Workspace (87%) and a budget shared-IP host (43%) is not a configuration problem you can fix. It is structural.
Google controls the largest receiving infrastructure in the world. A domain on Google Workspace is already pre-trusted by Gmail’s spam filters — the largest receiving service. Budget hosts are sending from shared IPs used by thousands of customers, some of whom have poor list hygiene. If a neighbouring sender on your shared IP gets blocked by Spamhaus, your IPR drops too.
The business impact at volume
At 100 emails/month: a 16-point IPR gap (Google vs Zoho) = 16 missed messages. Noise. At 1,000 emails/month: = 160 missed messages. Significant. At 5,000 emails/month: = 800 missed messages. A cost justification in itself.
For a 5-person team sending 50 client proposals a month, the difference between 87% and 50% delivery is 43 landed proposals vs 25. The buyer never sees the 25 spam-foldered ones to complain about.
Related concepts
IPR is affected by SPF, DKIM, and DMARC configuration — the deliverability triple lock. A correctly configured domain improves IPR; a misconfigured one depresses it regardless of provider.
Sender reputation is the aggregate score receivers use to decide where your mail lands. IPR is the output; sender reputation is a primary input.