I made a short post related to the goal of Inbox Zero about a year and a half ago but must confess that I have not spent much time in that semi-mythical land of digital organisation. The problem of lingering messages afflicts both my home and work mailboxes but I have recently hit upon an approach for the latter that seems to be heading me in the right direction.
I use a virtual pinboard (an Inkscape drawing) to keep tabs on my tasks, using colour and position to move them from active to the back burner patch or pending action from someone else. I now have devoted a corner of that to post the number of emails in my inbox at the start of the working day. My goal is simply to have less emails than that waiting at the end of the day. I started shortly before Easter at just below fifty; now I am beginning to dive through the mid-twenties with the teens in my sights.
It does get harder as I gradually pick off the easier entries from the long term inhabitants of the inbox but, countering that, anything that has been lurking in there for months tends to be less relevant on closer examination. If it continues to work, I will have to turn my attention to my home inbox too, which has also been hovering around a similar starting point of just below fifty.