I tried Sanebox and really liked it but today cancelled my account. I was only using it in my gmail which has a lot of crap emails which are almost spam-like (especially since I have a lot of people from overseas emailing me to be interested in their goods -- I mistakenly went to the Guangzhou Trade fair a few years back and handed out my business card!)
Sanebox created a separate label for in gmail and filed lots of my newsletter type emails and junk mail into the box which was great. I then got a digest email at some point in the day (check your timezone settings as if you set it up right it will send it at the end of the day) which pointed me back to the sanebox. This then enables you to train your contacts so that the email gets treated in the correct manner.
It did save me time and it did save me brain 'time', but I also missed a couple of emails which would have been better had I responded to in a more timely fashion. My email isn't that out of control so I've decided that I just need to be more disciplined and create filters and unsubscribe from more things.
I like the digest but it would work a lot better if I could process straight from the digest rather than having to go to another interface (webpage) to do it.
What I really need (and I think zeromail does) is the ability to mark an email as "unsubscribe" (in a very easy way like a short cut key!) and have it unsubscribe me in the background. Maybe zeromail is a service I need to try.
One thing that would be really cool from any service is the way to manage 'out of date' emails and auto delete or auto archive them when they expire. Things like deal-a-day (Zazz) or job alerts or my Google calendar which I send to myself on a daily basis would be great if they can sit in my inbox for the relevant day (allowing me to read/review and even delete it) and once it 'expires' (the following day) it disappears out of my inbox. Hopefully zeromail does this or maybe gmail already has the functionality and I haven't found it yet.
I find accessing my email on my phone helps me clear out a lot of the junk anyway as I can just tick and mark and mass delete or mass archive.