I leave everything in unread until I've dealt with it (sometimes I read something and if it can wait I mark it as unread again).
I worry if I put things in folders I won't be able to find something as it will involve searching multiple places, have I misunderstood how it works?
I'm a freelancer and often work with the same people (not necessarily for the same client, they are freelancers too), so that adds to my confusion on how to file.
I know there are email clients that are supposed to help with productivity, but they seem baffling!