I don't know if this will be helpful or not. I'm also a professor and basically process my e-mail Inbox to zero about four-five times a day. I keep the program turned off (pretty much) except for those specific times I check it or when I'm procrastinating.

I mark the e-mail that needs to be answered and move it to an "answer" folder. I set aside time about once a day to answer all those (that's usually about an hour of my day--usually in the late afternoon). I move the e-mail that requires me to do something (like set up a meeting) to a "Do something folder" and check that every couple of days (anything time senstive I put in my calendar to remind me). I move everything that includes something for me to read to a "To Read" folder and e-mail that I just need to keep around for a while to a "reference" folder. I check all of these at least once a week and clear out stuff that I don't need anymore.

I tell my students that they should expect me to take a least a week to read anything they send unless it's an emergency. Usually I get to it before that, but I don't want the expectation to be that I will. I also tell them that I respond to e-mail once a day and they can expect an answer to their e-mail within 24 hours except on the week-ends or holidays. I further tell that that if they send me a complicated e-mail, I will ask them to make an appointment for a face-to-face meeting.

I've been doing this for about a year and, unless I fall off the wagon and leave my e-mail open adn thus calling my name, I spend significantly less time on e-mail than I ever have before.