Definition
Email deliverability refers to whether your emails successfully reach the recipient's inbox. It is distinct from delivery — an email can be "delivered" (accepted by the receiving server) but still end up in the spam folder or be blocked entirely.
Good deliverability means your emails consistently land in the inbox where recipients can see and engage with them. Poor deliverability means your messages are filtered out before they ever reach your audience.
Formula
Deliverability is not a single formula but is measured by inbox placement rate:
Inbox Placement Rate = (Emails in Inbox / Total Delivered) × 100
| Variable | Description |
|---|---|
| Emails in Inbox | Emails that reached the primary inbox folder |
| Total Delivered | Emails accepted by the receiving server (not bounced) |
Average Benchmark
Inbox placement rates vary by sender reputation and industry.
| Metric | Average |
|---|---|
| Overall inbox placement rate | 85% - 95% |
| Good senders (high reputation) | 97% - 99% |
| Poor senders (low reputation) | 50% - 70% |
| Spam folder placement | 2% - 10% |
| Missing / blocked | 1% - 5% |
A healthy deliverability rate is 95% or higher. Rates below 90% indicate issues that need immediate attention.
How to Improve Deliverability
- Authenticate your domain: Set up SPF, DKIM, and DMARC records. These prove you are authorised to send from your domain and are the most important technical factor in deliverability.
- Monitor sender reputation: Check your domain and IP reputation using tools like Google Postmaster Tools, Microsoft SNDS, and Validity Everest.
- Clean your list regularly: Remove inactive subscribers, hard bounces, and spam traps. Sending to stale addresses damages reputation.
- Use a consistent sending volume: Avoid sudden spikes in email volume. Gradually warm up new IPs and domains by sending low volumes and increasing over several weeks.
- Manage complaints: Keep spam complaints below 0.1% (1 complaint per 1,000 sends). Make unsubscribing easy and visible in every email.
- Avoid spam trigger words: Words like "free," "guaranteed," and "act now" in subject lines can trigger spam filters when used excessively.
- Monitor blacklists: Check if your domain or IP appears on any email blacklists (Spamhaus, Barracuda, MXToolbox).
Example Calculation
If you send 50,000 emails, 45,000 reach the inbox, 3,000 go to spam, and 2,000 are missing or blocked:
Inbox Placement Rate = (45,000 / 50,000) × 100 = 90%
Spam Rate = (3,000 / 50,000) × 100 = 6%
Missing Rate = (2,000 / 50,000) × 100 = 4%
An inbox placement rate of 90% needs improvement. The goal should be 95% or higher.
Related Glossary Terms
A/B Testing
A/B testing in email marketing is the practice of sending two variations of an email to a small sample of your list to determine which version performs better before sending the winner to the remaining subscribers.
Abandoned Cart Email
An abandoned cart email is an automated message sent to customers who added items to their online shopping cart but left without completing the purchase. It is one of the highest-converting email types in ecommerce.
Abuse Complaint
An abuse complaint is a report from a recipient who marks an email as spam, which negatively affects sender reputation and deliverability.
AIDA Model for Email
The AIDA model (Attention, Interest, Desire, Action) is a classic copywriting framework used to structure email campaigns that guide subscribers from awareness to conversion.
Alt Text
Alt text is the written alternative to an image in an email, displayed when images are blocked, slow to load, or consumed by screen readers.
AMP for Email
AMP for Email is a Google-developed framework that allows email messages to include interactive elements like forms, carousels, accordions, and live content. It turns static emails into dynamic, interactive experiences directly inside the inbox.
Frequently Asked Questions
Delivery means the receiving server accepted the email. Deliverability means the email landed in the inbox. An email can be delivered but still end up in spam. Deliverability is the more important metric because emails that go to spam are rarely read.
Improving deliverability takes 4 to 12 weeks of consistent good practices. Focus on list cleaning, authentication, complaint management, and gradual volume increases. Reputation builds slowly and can be destroyed quickly, so consistency is key.
Yes, but less than sender reputation and authentication. Spam filters analyse content for suspicious patterns, excessive links, all-image emails, and spam trigger words. However, even well-written emails will have poor deliverability if the sender has a bad reputation.
The three main protocols are SPF, DKIM, and DMARC. SPF authorises which servers can send email from your domain. DKIM adds a digital signature to verify the email has not been tampered with. DMARC tells receiving servers how to handle unauthenticated emails. Implementing all three is essential for good deliverability in 2026.
Yes. New domains and IPs have no reputation with mailbox providers, so start with low volumes and gradually increase over 4-8 weeks. Send to your most engaged subscribers first. Monitor bounce and complaint rates closely during warm-up. A sudden spike in volume from an unknown domain will trigger spam filters and hurt long-term deliverability.