The mailboxes commanded by these millions of users were estimated to number about 1.4 billion in 2006.
Corporate Users
The Radicati Group counted 516 million business email inboxes worldwide in 2007.
Naturally, all numbers are educated guesses. I don't know the exact methods used to arrive at them. Still, they are probably more educated a guess than most of us can make.
How Many Emails?
The millions of email users send hundreds of billions of messages every day.

