Hello @WilliamP2367 ,
I'll be moving this post from our Product Ideas board to our Questions & Discussions board, since it fits better there.
For info regarding the Engagement metrics used for the pre-built segments and contact insights, I'd recommend checking out our main article on the topic. Engagement is just a weighted, algorithmic measure of your contacts' opens and clicks against your send regularity.
I'd also recommend these articles if you're looking for additional ways to manage your contacts, based on our engagement scaling:
Find your contacts by their engagement level using segmentation
Re-engage contacts who aren't reading your emails
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As far as trimming up your contacts, the first step I always recommend is deleting bounces we recommend for removal. Whether they're blocking emails from us, their network is constantly telling us they don't exist, or they've been suspended after you and/or other customers of ours have attempted to send and been repeatedly bounced back, these contact won't be viable to send to.
The next would be using segmentation, whether it's the pre-built low engagement one or one you manually create, to get a solid set of contacts that haven't regularly been engaging with your material via opens and clicks. If doing it manually, you'd set it based on Contact Activity > Did Not Open > and then set it for either your last 5 emails or any within date range. Doing it manually will also allow you to set other parameters, such as only targetting unengaged contacts in specific lists, with certain tags, etc.
You can then further manage this segment by adding it to a list, going into the list and removing contacts haven't even had enough time to properly engage (such as very recent additions based on Date Added), and then either attempting re-engagement and/or deleting all the remaining least engaged.
If, after making an honest attempt to utilize the engagement resources and re-engagement advice, you're unable to keep up with it, only then would I recommend contracting our professional services to handle it for you.
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William A
Community & Social Media Support