What is an open rate?

The open rate is a measure of how many people on an email list open (or view) a particular email newsletter or campaign. The open rate is normally expressed as a percentage, calculated as:

So a 40% open rate would mean that of every 10 emails delivered to the inbox, 4 were actually opened.

How do you measure an open?

Recording an ‘open’ can only happen if the reader's email client is capable of displaying html. So if you are sending text-only emails, there is no way to record open rates (the exception is if they actually click a link). Similarly, people reading your html email without images showing will not be recorded as opens.

Another issue is that your readers may have a preview pane in their email client. That preview pane might be displaying your email automatically (and therefore downloading the images) without the reader ever having to click on it or read it.