This is such an alien problem to me thar I can even begin to imagine a person who truly cannot manage to consistently go through their emails.
Either you are a super important person, at that point all those emails could also be quite important (so read them!), or you have lots of notifications, CC and other emails merely for future reference, which can be either filtered automatically or deleted.
If your slack channel sends you a summary every X unread messages, either you care or you disable that.
If medium sends you updates every day, either you want to be daily updated or you unsubscribe that.
For me, it’s a matter or knowing I have gone through everything. I use unread (since they show in bold on top) as my ‘to do’ list.