Open rate is the percentage of delivered emails recorded as opened. An open is recorded when a tiny invisible tracking image in the email loads from the sender’s server. The usual formula is unique opens divided by delivered emails, so someone who opens the same email three times counts once.
Open rate was once the headline metric of email marketing, but it has become much less precise. Apple Mail Privacy Protection loads images automatically for many Apple Mail users, recording opens that never happened. Some security filters do the same. On the other side, people who read with images turned off, or in a text-only view, don’t register at all. The figure you see is an approximation, and for many audiences an overestimate.
It is still useful when read carefully. A sudden fall in open rate across several campaigns, especially at one mailbox provider, can be an early warning that mail is going to spam. Comparing opens for two subject lines sent to similar audiences on the same day can still guide you. What it can’t do is tell you exactly how many people read your email, or which subscribers are truly engaged.
What improves real opens hasn’t changed: a recognisable sender name, a subject line that tells people why the email is worth their time, a preheader that adds to it, sending when your audience checks email, and a history of sending emails that were worth opening. Inbox placement matters most of all, because emails in spam are rarely opened.
A Surat diamond jeweller’s newsletter shows a 38% open rate but only a 1.2% click rate. Splitting opens by provider shows that Apple Mail users open at nearly 70%, a sign of automatic opens. The team starts judging campaigns on clicks and enquiries instead.
MailNesto reports unique opens alongside clicks and click-to-open rate, shows opens by city on a map, and lets you send to each contact at their usual opening hour.