The magnetic pull to check your email every 10, or 5, or 2 minutes will kill you. Not literally, of course. As far as I know, your personal health won't suffer from peering into your inbox like a cat into a fish tank. But the relentless pull of the inbox on your attention will almost certainly prevent you from attending to what's really important to your customers and your company.
It's important to realize that processing email is a piece of work in and of itself. As Merlin Mann elegantly expressed it, processing is more than just checking, but less than responding, to every email. You have to read and assess each email, and then determine what you're going to do with it. That may mean replying, but also may mean deleting, or filing, or designating time at a later date to deal with it. "Processing" takes time.
All too often, though, we'll check our email on our way out the door when we only have two minutes to process our inbox. Or when we're in the middle of some other task with a pressing deadline, and we really can't spend much time. We're looking for something important or urgent -- a priority item that we can take care of right now in the two minutes we have available. We ignore everything else in the inbox as we get sucked into the priority trap.
And this is the road to the inbox with 19,327 items in it, 1,738 of which are unread. Because when you fall into the priority trap, you don't make the time to fully process all those messages. And each time you look just for the high priority email, the messages that arrived earlier cross the river Styx of your monitor's bottom edge and get pushed into the grey netherworld below the fold. You'll never find those messages again either, because if you haven't processed them, you won't remember them. And if you don't remember them, no amount of sorting by sender or date will help.
Why is this important? To cite one example, in 1999, NASA's Mars Climate Orbiter burned up in the Martian atmosphere due to a colossally stupid blunder. Apparently, there were two teams of engineers working on this project, one in English units, the other in metric units. Inconvenient, but not catastrophic, as long as they reconciled their calculations. Alas, they never did, and we ended up with a very pretty fireworks display over the Valles Marineris. And here's the kicker: the flight director had an email buried in her inbox addressing this very problem. Presumably, she had seen the email, but it wasn't a priority at the moment she saw it (it was 10 months from launch to fiery finish), so she never processed it. It simply slid off the bottom of her screen into oblivion. Not to put too fine a point on it, but that was a $327 million email.
We need to establish standard work for processing email. The reflexive, unthinking, 120 second "checking" of email just won't cut it. Whether you handle email once a day, twice a day, or every hour doesn't matter -- but for god's sakes, process it. Don't "check" it. Give yourself enough time to deal with all of the messages. Whether that's 10 minutes or 30 minutes is up to you, but don't go into your inbox unless you have that time for processing.
Obviously, there are circumstances when your only option is to triage your inbox -- you only have time to look for a truly urgent item that needs your attention. But treat those instances as the exception (the variation from standard work), rather than the rule. Otherwise you might lose a $327 million email in your own inbox.