The United States topped the list, followed by South Korea, China (including Hong Kong), France and Brazil.
To compile the list SophosLabs scanned all spam messages which were received at the company's global network of spam traps, according to a statement.
More than 60 percent of spam came from zombie computers -- hijacked PCs which were infected by malware -- allowing culprits to send spam to innocent computers in any country, Sophos said.
Rob Forsyth, managing director for Sophos Australia and New Zealand, said that it was good to see Australia slipping off the dirty dozen spamming countries list.
"The combination of legislation, education and software appears to be winning the local battle against spam," Forsyth said.
Sophos' research also found that North America still accounts for almost 30 percent of all spam.
However, the US and Canada had reduced their contribution to spam by nearly 20 percent in the past year, it found. There were a range of reasons for this decrease, Sophos said, such as jail sentences for spammers, tighter legislation and better system security.
Graham Cluley, senior technology consultant for Sophos, said efforts such as ISPs sharing knowledge on how to crack down on spammers, and authorities enforcing the US CAN-SPAM legislation, had helped North America tackle the spammer.