Dive summary: 

• Spam's share of email traffic hit a five year low in 2012 due mostly to email filters and protection. 
• Spammers changed tactics in 2012, moving from posing as hosting services and social networks to airlines, hotel reservation sites and coupon services such as Groupon. 
• The US and China hold the top spot for malicious emails because the countries' large servers are attractive to spammers. 

From the article: 

"... Most of the spammers are home-grown. The spam originating in the United States increased 13.5 percentage points, coming in second place. While China, which wasn’t even on the top 20 sources of spam in 2011, is the new number one!

Both countries have both previously been leading sources of spam. But after anti-spam laws were passed and botnets were shut down, junk mail coming from these countries decreased. Clearly, spammers still want to take advantage of the powerful computing resources available in the U.S. and China to set up new botnets in those countries, according to Kaspersky Lab’s guesstimates. ..."