I get a lot of email, and about once a quarter I sit down and go through my email, archiving the stuff I no longer need (I haven't thrown away an email in 20 years) and deleting everything else. I also take the opportunity to sort out my auto-filing rules. Every email from a known source goes into an appropriate folder, anything else gets lumped into a folder so that I can check its content and move it to the Spam reporting folder, delete it, or manually move it into the right place. If I've got a new client, or subscribed to some new mailing lists then I'll add them to the rules.