What is the volume of e-mails on the global internet?

I need an estimate of e-mail volumes (number of e-mails, not bytes),
ideally globally but will settle
for USA only.  Number of e-mails sent per day or month.

I need a reference to a published estimate.  An estimate from one of
the industry analysts (Gartner, Forrester, Datamonitor, ...) would be
ideal, any recognized name (BBC, CNN, ...) would be great, but I'll
settle for almost any number you didn't just make up.

Data from 2002 or later is required.  There is no need to separate
different types of e-mail (eg spam v non-spam).

Hi cybaea,

Thanks for your question!

The International Data Corporation estimates that in 2002, 31 billion
emails were sent each day, worldwide.

The relevant press release, which includes email volume predictions to
2006, can be viewed at
<http://www.idc.com/getdoc.jhtml?containerId=pr2002_09_23_113035>.

I used the following searches to find your answer:

number of emails sent in 2002
number of emails sent per day worldwide
number of emails sent
idc email statistics

All the best!

Emjay-ga

Excellent - just what I needed.  Thanks.