An inactive subscriber is a newsletter’s subscriber from whom no action (opening or click) has been observed during a given period of time.
Inactivity criteria vary from one newsletter to another according to the activity. A relational newsletter with a brand building goal can thus be effective without generating any clicks.
High proportion of inactive subscribers can be an issue for deliverability with behavioral filtering used by webmail and ISP.
The inactive subscriber’s status must usually be checked by a reactivation campaign. Indeed, a non-opening newsletter can be a partial result of messages reception with blocked images.
Most of inactive subscribers are generally called ghost subscribers.