For some reason, email hasn't changed fundamentally since it's original inception back in the computer dark ages of un-powerful PCs running over slow networks. It is basically a text-based protocol with no security whatsoever. You can spoof who the email is from and read any of them with a network sniffing tool. Everything since then has been tagged on the top like PGP for security, IMAP for mail servers, Exchange Server (whatever that adds). Basically I don't like email because it has few useful features and it is extremely over-used for a variety of tasks that it is definitely not suitable for.
In terms of functionality, I would like a feature to be added to email which is simply an "expiry" date. Many emails that are sent are only relevant for a period of time (long or short) and the ability to allow the email systems to delete expired mail would clear logs of unnecessary backlogs. For instance, using an email to tell you that a backup succeeded or failed is mostly irrelevant after the next backup occurs so if you get 10 of these over the weekend, probably 9 of them can be discarded. However, I do not have the influence to make that happen but I do have an influence over how I use email and require others to use it.
My old manager had something like 5000 emails in his inbox. He was an extreme example of badly used email. What is the point of having that many when you can only handle a few at a time? Here are some suggestions as to why he had too many and what you can do to avoid the same mistake:

  1. Self-importance! If you think you are too important, you want to be copied in on everything. This betrays major issues either with trust or just how badly the organisation is run.
  2. Incorrect use of email. Having emails for things like successful backups is perhaps acceptable if you only have one server and it backs up once per day but really, there are proper tools that monitor these things and which don't need to spit out tonnes of emails into your inbox. A monitoring system that has to send emails constantly to convince you it is running is not really much good!
  3. Incorrect use of email too. Lots of people claim they write emails to leave a 'paper trail' of decision making to cover their backs later on. This is tosh. Whatever you have written in an email is likely to be mis-construed which is a defence later on when someone decides that you didn't tell them to do X in the email. Pick up the phone if that's what is required. You can communicate 10 times more efficiently with your voice (and even more in person) than you ever can on email. Why take 10 minutes to try and formulate what you could describe and discuss in 30 seconds? If someone doesn't understand, they can ask you straight away rather than writing you a 10 minute reply!
  4. Make correct use of importance and expiry. Although expiry is not part of the email standard per-se some providers give you an expiry option which allows you to mark an email like "you have left your headlights on" to expire after 4 hours and not to be looked at by everyone who has been on holiday for 4 weeks.
  5. Use correct subjects. Your subjects should be very concise, especially on emails going to more than one person since some of those people might very much not be interested. An email with a subject like "Does anyone have a set of jump leads" is more useful than one with a subject of "request" and a body that contains the question.
  6. Consider alternatives. Sometimes you could write your own application to do something that you currently use email for (such as monitoring backups, lift sharing or general enquiries). You could use a separate system (like Yammer) to allow people to ask non-work related questions to keep your inbox down. Also, an email like "Potatoes are ready" being sent every day at lunchtime can be annoying. How about telling people that the potatoes will always be ready at 12 unless there is an email to the contrary?
I heard about the head of a car company who had banned his employees from using email for the fact it is really inefficient. Will be interesting to see whether they can break the email mindset!