Email Deliverability

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 Tools

• Email Deliverability Calculator: Assess your deliverability at email deliverability calculator
• Email Deliverability Loss Calculator: See how much revenue poor deliverability costs you at deliverability loss calculator
• Spam Complaint Rate Calculator: Track your complaint rate at spam complaint rate calculator

Frequently Asked Questions

What is the difference between delivery and deliverability?

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.

How long does it take to improve deliverability?

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.

Does email content affect deliverability?

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.