Do you find yourself being overwhelmed by the amount of email flowing into your inbox? Here are some tips I've used to keep my inbox nearly empty over the years. And most of these tips extend to your real-world and voicemail inbox as well and will (I think) help you remain more sane and organized (and polite).
1 - Do not subscribe to email lists that you are not actively interested in. This seems obvious to some people, but if you find yourself just deleting every message from a particular email list, newsletter, or other source of emails, just unsubscribe. Maybe you were really keen on the particular subject at the time you subscribed; maybe you thought it'd be neat to stay on top of X, but if you find that's just not the case--that it's not important enough to you to do so, just cut it out; you can almost always subscribe again later if you get interested.
2 - Think of your inbox like a to-do list; it already is in a certain sense, but make it more formal in your head. Anything in your inbox needs attention, and it needs it as soon as you can get to it. The reason this is helpful is that it can help motivate you to not let things pile up. It also lends towards other helpful things like the next tips.
3 - Try to take action on every email as soon as you read it. If it requires a response, try to respond right away. If you need to think on it, it's okay to leave it there for the next pass. If you think it will be a while until you can respond like you think you need to and the missive is personal (from a real person to one or few persons), respond right away saying you're thinking about it and give a timeframe within which you intend to respond. This is just polite and will probably save you from getting more emails from that person asking for a status. If it is something from a list or newsletter that you are interested in, leave it there for the next pass.
4 - I mentioned the next pass in the previous tip. This is simply a way of further weeding out your inbox, especially for non-personal emails. If you truly didn't have time to properly take action on the first pass, the next time you sit down to look at your email, give everything a second look. This takes far less time, typically, than the first pass, and allows you to quickly determine if you feel you can take action on the second pass items. By the second pass, you should have taken action on 80% or more of the emails in the previous first pass. Yes, I'm making the percentage up, but I'm just pointing out that if you're finding most emails in the inbox survive the second pass, you're probably not devoting sufficient time to it. .NET developers can liken this process to .NET garbage collection, if emails survive the first pass, they're promoted to gen1, and so forth. But the higher the generation, the fewer remaining emails there should be.
5 - Aggressively delete. Be willling to decide that you just are not going to get to something and either file it away or, preferably, delete it. This only applies to non-personal emails that don't require a response (e.g., the newsletter/email list variety). You may think that you'll get time some day to look at it, but I assure you, if it reaches the third pass and is still not important enough to make time for, you probably never will make time for it. In my opinion, the only things that should survive the third pass are items that truly require action on your part but that may require more time than the average email response. For instance, if you get a bill reminder, you can't just choose to delete and ignore that, but you may not have time until, say, the weekend to get to it. It's fine to just let these lie, but leave them in the inbox so that you don't forget. You should have very, very few emails that survive the third pass. If you have lots, you're not giving your email enough time.
6 - I should mention that in the last three tips, there is implied prioritization. In my book, emails from one person directly to you should always take precedence, even if you're not particularly keen on it (e.g., if someone is asking you for help, which happens for folks like me who publish helpful stuff). I consider it rude to ignore personal emails, even from recruiters, so I always make an effort to respond, if nothing else than to say that I'm sorry that I don't have time. To me, this is just common sense politeness, and I hate to say it, but it really irks me when folks don't extend the same courtesy to me. The good news is that if you follow my tips, you can continue to be a polite person, at least in that regard, because your inbox never gets so full that you don't have time at least for the personal emails. (And by "personal" I don't mean non-business; I mean from a real person to a real person, so business-related missives are not excluded from this rule.)
7 - Check your email proportionately to how often you get personal email. It's okay to let newletters and lists pile up because you can safely delete huge swaths of those if they get piled up, but it is not okay (IMO) to let personal emails pile up. If that's happening, you need to check email more often and/or make more time for it. Maybe it's not your favorite thing, but it is just part of life. If you're important enough, get someone to screen your emails for you.
If you follow these guidelines and still find your inbox piling up, you're either really, really important and famous, or you're just not being honest with yourself about what you do and don't have time for. If nothing else, find a way to stay on top of the personal email. Even if you don't like my approach to everything else, it is just the polite thing to do.