The open rate differs from send rate in that it will tell you what percentage of senders will read your email (aka how often your email is opened), rather than just receiving mail and scan.
Calculation: Open rate = Total emails opened / (Email sent – Email bounced)
Email open rate help many marketers to measure the success of campaigns. However, it’s an unreliable measure because an email is only counted “opened” if the recipient also receives an attached image. Besides, most email users block viewing permissions. This means that even if they open the mail, they won’t be counted towards the Mail Open Rate, making it skewed and an unreliable metric for marketers, as it reports a lack of numbers, amount of mail opened.
Also, email open rate can be manipulated by compelling writing or a highly emotional subject that causes email recipients to open the mail, only to feel deceived by the content later. For that reason, it is better to focus on Click-through Rate (CTR), an excellent tool for measuring successful emails.
Read more: Ways to Improve your Email Open Rate