As a first step, you need to define what “active contact” means because it will decide how your filter is done. Indeed, there isn’t only one definition and it can change depending of your company's context. Each user has its own way to specify it, which could be with an opening, a click or a purchase.
However, we have noticed that a target of active contacts is generally measured with a 3 months delay, which means contacts must have at least one opening the past three months.
With a filter, this can be applied with the following conditions:
|Openings in 3 months||>||0|
In the same way, we can call inactive contacts those who didn't opened an e-mail during the past three months:
|Openings in 3 months||=||0|