...it's the amount I send.
This was brought home to me five minutes ago. I'm sat at home, digging my way out of my inbox (trying to reach Zero Email Bounce), and somehow I ended up in my Sent Items folder. "Wow", I thought, "that seems kinda full".
One Outlook search folder later (sent:today from:me) and I'm stunned to find that I've sent 47 emails today. Of those, 45 have been work-related. I'd need to average one email every 10 minutes, with another 10 minutes off for lunch, to send those during an 8-hour work day. And yet I also squeezed in three meetings, several hallway discussions, and some work on our team infrastructure.
At least now I know where the day went.
(If you want to learn how to cope with incoming email, I like Stever Robbins' "Tips for Mastering E-mail Overload" and Ole Eichorn's "The Tyranny of Email". If anyone knows how to cut down on sending email, I'm all ears. Although "stop working with interesting projects and passionate people" isn't an option!)