When do you prune your bulk e-mail subscriber list?

Best practice is to have it driven by each user's activity level.

I have a list of the same size, and when a user hasn't opened or clicked any of the last 15 to 20 emails, then I just remove them. You could try a re-engagment campaign if you want, but it has never seemed worth the effort to me.

If someone hasn't opened any of your last 20 emails, why would they open the 21st? And what are they odds they would actually pay for something? Pretty small.

So I just prune them and focus more on getting new leads. An email list is never static. It's a living, breathing thing that needs growth and pruning.

What I would do:

• Set up a new segment for disengaged subscribers. After three months of no engagement, add subscribers to this segment.
• Set up a re-engagement campaign. Soft touch, less sales, more brand and content focused.
• At the end of the re-engagement journey, anyone who hasn't engaged at all, I would segment again into a 'ready for delete' list and have them sit there for another month or two and then delete them. This is purely to allow the disengaged subscriber time to open your emails if they're busy or only check intermittently,but also gives you an easy way of removing completely disengaged subscribers.
• Everyone who engaged with at least one of the emails, gets removed from the disengaged segment.

I would try and automate this process in your platform, as this can be a lengthy process.
Cleansing your list intermittently is imperative to a healthy sender reputation. We shouldn't be scared of unsubscribing people if they aren't showing any interest.

What do you use to track your email subscriber numbers? Also how do you know how many have opened them?