Open Rate / Deliverability

Open rate is the percentage of delivered emails that recipients open. Deliverability is the measure of whether your emails actually reach inboxes instead of spam folders. Open rate tells you how engaging your email is. Deliverability tells you whether anyone gets the chance to engage at all.

Category: Marketing Automation (also: Analytics)

Author: Atomic Glue Editorial Team

## Definition

Open rate is calculated as the number of unique email opens divided by the number of delivered emails (excluding bounces). It is tracked using a transparent 1x1 tracking pixel embedded in the email. Deliverability refers to the ability to successfully land emails in the recipient's inbox rather than the spam folder or being blocked entirely. These two metrics are deeply connected: poor deliverability means fewer people see your emails, which suppresses open rates. Poor open rates signal to ISPs (Gmail, Outlook, Yahoo) that your emails are not wanted, which hurts deliverability. Together, they form the core health metrics for any email marketing program. A 40 percent open rate means nothing if only 60 percent of your emails reached the inbox.

## How Open Rates Are Measured (and Why They Are Unreliable)

Open rates are tracked by an invisible pixel in the email. When the recipient's email client loads the images, the pixel fires and registers an open. This makes open rates unreliable for three reasons: image blocking (many email clients block images by default), preview panes (loading the email in a preview pane may register a false open), and Apple Mail Privacy Protection (which pre-loads images and inflates open rates). Despite these limitations, open rates remain the standard metric for subject line testing and general engagement comparison.

## The Three Stages of Deliverability

Deliverability has three stages. **Delivery**: the email is accepted by the recipient's mail server. **Inbox placement**: the email lands in the inbox rather than spam. **Engagement**: the recipient opens, clicks, or replies. Most email platforms report delivery but cannot report inbox placement without third-party tools (like Litmus, Everest, or GlockApps). Inbox placement rate is the true measure of deliverability and can be significantly lower than the delivery rate shown in your ESP.

## Factors That Affect Deliverability

Sender reputation is the primary factor. ISPs evaluate your sending domain reputation based on complaint rate (spam complaints per 1,000 emails), bounce rate, unknown user rate, spam trap hits, and engagement metrics. Authentication protocols (SPF, DKIM, DMARC) are required by Gmail and Yahoo as of 2024. List hygiene matters: regularly remove inactive subscribers and hard bounces. Content quality affects deliverability: spam trigger words, high image-to-text ratio, and too many links can trigger spam filters. Sending consistency matters: sudden volume spikes are suspicious.

## Improving Open Rates

Open rates improve when emails are wanted. The single biggest factor is list quality: engaged subscribers open emails; disengaged subscribers do not. Subject line testing (length, personalization, curiosity gaps) can improve open rates by 10 to 30 percent. Preheader text (the snippet after the subject line) is almost as important as the subject line itself. Sender name recognition matters: emails from a known person or brand open at higher rates. Send time optimization based on audience behavior also helps, but gains are typically smaller than list quality improvements.

## Note

Apple Mail Privacy Protection (MPP) has made open rates less reliable. MPP pre-loads email content, including tracking pixels, which artificially inflates open rates for Apple Mail users (who represent 40 to 60 percent of many B2B lists). Use click-through rate and reply rate as supplementary engagement metrics.

## Common questions

Q: What is a good deliverability rate?

A: A healthy inbox placement rate is 95 percent or higher for permission-based email. Rates below 90 percent indicate significant deliverability problems that need investigation.

Q: How often should I clean my email list?

A: Remove hard bounces immediately. Remove unengaged subscribers (no opens in 90 to 180 days) quarterly. A smaller, engaged list outperforms a larger, stale list on every metric that matters.

Q: Does email frequency affect deliverability?

A: Yes. Sending too frequently increases unsubscribe rates and spam complaints. Sending too infrequently causes subscribers to forget they opted in, increasing the chance they mark you as spam. Find the frequency that maximizes engagement for your audience.

## Key takeaways

• Open rate measures engagement; deliverability measures whether emails reach inboxes.
• Deliverability requires attention to SPF, DKIM, DMARC, list hygiene, and sender reputation.
• Apple MPP has reduced open rate accuracy; supplement with click and reply rates.
• List quality is the single biggest driver of both deliverability and open rates.
• A healthy inbox placement rate is 95% or higher.

## Related entries

• [Email Marketing](atomicglue.co/glossary/email-marketing)
• [Email Automation / Drip Campaign](atomicglue.co/glossary/email-automation-drip-campaign)
• [SPF / DKIM / DMARC](atomicglue.co/glossary/spf-dkim-dmarc)
• [Marketing Automation (HubSpot / Marketo)](atomicglue.co/glossary/marketing-automation)

Last updated July 2026. Permalink: atomicglue.co/glossary/open-rate-deliverability