I think in reality many who even opt into receive emails don't read stories that aren't of interest to them, but as you say they've seen something they like rather than just random people being added. I know opt-in's are tricky because for everyone who didn't opt in to receive emails, they need an opt-out option and that's a legal requirement. Also different countries have different data protection laws - such as CanSpam in USA but not Canada and GDPR in Europe. Care is definitely needed not to violate anyone's rights. Technically if they didn't opt in, they must be able to easily opt out, the same as if they had opted in. At least easy opt-out lets them opt out of receiving emails.

I agree that many email addresses maybe just data and nothing else, the same as followers who aren't really interested in our articles, or maybe aren't even members. Random emails or followers isn't good and better not to have them at all. I think genuine followers also will find our stories if they are interested in them - so customisation could also apply to followers, as much as email subscribers. It would be a good idea to look at who follows and if they regularly contribute or read our stories and if so which ones and try to write stories they will be interested in, as well as potentially get new followers. I think the "one size fits all" model makes customisation difficult, as not every subscriber or follower will be interested in our stories and it's impossible to customize for everyone.