Open rate
The share of delivered emails recorded as opened, measured with a tracking image that loads when the message is displayed, and distorted by privacy features and scanners.
What it means
An open is counted when a tiny, transparent image in the message is downloaded. Mailchimp describes its open rate as the percentage of successfully delivered emails that recipients opened, counted this way.
The method has two blind spots. A client that does not load images records no open even when the message was read. Software that fetches the image without a reader records opens that never happened: Apple Mail Privacy Protection prevents senders from seeing whether a message was opened, Mailchimp warns that bot activity such as MPP can falsely inflate opens and clicks, and M3AAWG notes that spikes in opens or clicks may come from security appliances examining the mail.
Use open rate to compare similar campaigns, not as proof of reading, and combine it with clicks, replies and purchases before acting on it.
Related terms
On this site
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- Mailchimp: About open and click ratesmailchimp.com
- Apple Support: Use Mail Privacy Protection on iPhonesupport.apple.com
- M3AAWG Sender Best Common Practices, version 4.0 (August 2026)m3aawg.org
All 432 terms in the glossaryThe wiki: blocklists and bounce codes