Unsubscribe rate is the number of unique email addresses that do not wish to receive any further emails from you – People who opt-out of your mailing list. Unsubscribe rate shows how relevant the content was to the audience in the mailing list.
Unsubscribe rate = number of unsubscribed email addresses / list size
This rate should be low with a value between 0.3 to 1 %. Unsubscribe rate higher than 1% indicates that there is an issue which needs to be addressed.
Before people unsubscribe from your email list it’s nice to get their feedback on the reasons for unsubscribe. This would give you a better understanding on relevancy of the content and mailing list.
But, if the recipient wishes to unsubscribe, it is important to take action quickly because if the recipient marks you next campaign to ISP’s as SPAM this would hurt your reputation as a marketer.