I have one personal email (posteo, 1 euro per month) that I use for personal correspondences, and one shitty personal email I signed up for in high school that I use for anything where there's any chance it might make it to some corporate mailing list. I have the posteo address set up alongside work email to notify me when new mails come in, and the junk address I'll login through firefox like every few days (unless I'm expecting something specific) to skim and mark the most recent mail as read so I know where to start skimming next time.

For work, anything I actually need to deal with I'll mark as unread until I get around to it, because it's annoying seeing the icon show I have unread messages. Sometimes "getting around to it" does just mean putting it in a calendar or some other way of making sure I don't lose track.