After I’ve read it and taken the appropriate action with it, of course.
Not “Archive.” Delete.
I’ve stopped stashing emails in thematic folders. I have a bunch of emails related to the agenda for a committee meeting last October in a folder called “October Committee Meeting.” Why? The meeting came and went, and there is nothing more for me to do about it.
Delete the folder.
If an email remains undeleted, it pertains either to a project I’m currently working on (“January 25th wedding” for example) or it needs some further reply or action from me. A small amount of emails reside indefinitely in a folder I call “Reference.” Anything outside that range gets deleted.
It’s about focusing on what’s in front of me and carrying less.