July 4, 2011
Spam Decreased 82.22% Over The Past Year

On July 2010 when approximately 230 billion spam messages were in circulation each day, accounting for 90% of all email traffic. This has now declined to 39.2 billion messages per day, accounting for only 7.29% of all email. 

annotated graph of spam volume

Graph of spam volume, global estimated spam sent, billions of messages per day, 15th June 2010 to 14th June 2011.

Source: 
Symantec