Open rate refers to the number of HTML message recipients who opened your email and is usually calculated as a percentage of the total number of emails sent. The open rate is considered a key metric for judging an email campaign's success.
However, as a metric, the open rate has several shortcomings:
- The open rate compares the number of emails opened to the total number sent, rather than to those that were actually delivered.
- Opens cannot be calculated for text emails, because image downloads are the means used for tracking opens.
- Some email clients allow subscribers to scan message content without actually opening the message, which is not calculated as an opened message.