There’s something that I do with my emails that might work for you if a) you’re fairly good at assigning a reasonable (not too much, not too little) amount of work to yourself the day before the work has to be done and b) there’s a way to flag/star/mark certain cue items.
I have a goal called “Starred” for starred emails. At the end of the day (which is past the Beeminder deadline for the goal), I go through my inbox and star emails that I want to work on by the deadline tomorrow. Each starred email is a +1 in my Starred goal, and then, on the day of, I go through and handle them and put a -1 datapoint for each once it’s been handled. The road rate is 0, so I have to come back to zero by the deadline by handling anything I starred the day before (and anything I star on the same day, which I occasionally do to force a quick turnaround on some emails).
I don’t know if that would be helpful for you, but it was helpful for me in the past, which is why I just restarted it a couple of days ago.