How many emails are sent each day?: From the Useless Trivia That We Love To Speculate On Anyway department.
VeriSign (the exclusive registry for .com and .net domains) estimates (PDF) that there are about 2.25 billion email queries per day. However, because of caching, email queries represent only a fraction of the number of emails sent.
[…] According to a CNN article, in 2001, the International Data Corporation (IDC) predicted the number of emails sent each day would exceed 36 billion by 2005. But in 2003, the IDC reported that 31 billion emails were already being sent daily, and they expected the number to double by 2006.