For every e-mail that gets sent, there's an inbox that probably can't handle yet another mail.
Cue the hipster trying to explain this "phenomenon": "I just get so much mail; I really can't answer all of them.", "So sorry if I missed your mail, but I get hundreds each day and yours probably fell through the cracks." or "E-mail overload is a real problem."
See, I get it: we're all struggling to answer all of our e-mails since every Tom, Dick & Harry started sending an e-mail about everything a couple of years back. And now most Tom's, Dick's and Harry's have smartphones too (just so they look cool, not because they necessarily fully grasp the device), so they're sending you mail while on the pooper. I get it.
I also know that answering e-mail - especially lengthy one's - isn't the most pleasurable experience, nor do you feel like you've accomplished anything after you're done. I also absolutely hate waking up to an inbox with 30 unread mails, which means I've developed a bad habit of answering a couple of them on my iPhone, in the bed before I doze off to sleep. Bad habit. Yuck. But we do what we have to do.
The best part is that the more e-mails you manage to respond to, the more you are likely to receive back. Exponentially. Talk about a catch-22.
Here's the MASSIVE BUT though: None of these makes it okay for us to start ignore e-mails.
If I sent you an e-mail, I most probably did so because I would really appreciate a response (of any kind). Or maybe I really look up to you, admire your work and wanted to connect about something that might just be important to me. I also sent you the mail knowing that you are busy (just as I am), that it might take a couple of days for you to respond (which I'm okay about) and I tried to keep the e-mail as short as possible in respecting your time. If you don't respond, I don't know whether you got my mail, whether it perhaps went to spam or whether you didn't regard me important enough to warrant a response.
I'm nowhere near perfect when it comes to answering my own mail, but I try really, really hard to answer every single e-mail that pops up in my inbox. I'm slightly obsessive compulsive when it comes to keeping my inbox clean, I don't use any computer process that will "prioritize" my mail for me (just another lame excuse not to answer e-mails from senders outside of my network) and I realize that this isn't the most productive decision I've ever mind. But common courtesy is still a value that I regard highly.
So to everyone moaning about not having enough time, you can join the rest of us in that boat. We can also seriously stop playing the "my inbox is bigger than yours"-game, since that doesn't get the e-mail answered either. We all agree that the massive amounts of e-mail that gets sent is a real problem, but we're not solving it by selectively ignoring some of those e-mails.
You're not doing anything wrong when you're not answering the mail you receive. Compare it having your own home; if there's a knock at the door, it's your choice to open it or pretend like you're not there.
I for one - and I'm sure I'm not alone - have much more respect for those people that takes the 2 minutes to reply to my mail.