One of the most important metrics in an email campaign is Email Marketing Open Rates. It is the number of recipients who have opened the email.
The open rate is the ratio of the number of recipients who opened or read the mail to the number of recipients the email campaign was sent to.
You also need to know the reason: why your subscribers are not opening your email. Once you know the reason then only you’ll be able to work on it and improve your open rates.
There are other important techniques as well to Improve Email Marketing Open Rates: