A man described by Microsoft as one of the top 10 spammers in the world has been sentenced to nearly four years in jail after pleading guilty to charges of fraud, spamming and tax evasion.

Robert Soloway, dubbed the Spam King, admitted to using a utility called Dark Mailer to send more than 50,000 emails an hour to internet users.

The software changed the headers of emails to that of the recipient's address to fool spam filters.

"I take full responsibility for everything I've done. I am sorry for all the people that got the emails," he said. "I am very embarrassed and ashamed."

Prosecutors had asked for nine years in prison, considering the scale of his activities and the fact that he had been caught spamming in 1999.

Soloway had promised to change his ways, but had simply moved to a different state and carried on as before.

"The government believes that it is important to recognise and pronounce publicly, and emphatically, that fraud in email is a serious crime," said the prosecution team. "The financial and societal costs of this crime are immense."

The defence team argued for leniency as Soloway's software did not interfere with individual PCs, did not try to spread malware and never advertised pornography.

Soloway will also serve three years probation and do 200 hours of community service. Prosecutors wanted to seize $705,000 in property but Soloway maintains that most of the money has already been spent.

Microsoft has also won a case against Soloway and been awarded $7.8m in a civil case, but is unlikely to see any financial reward. An American ISP has also been awarded more than $10m in a similar case.

It seems likely that Soloway will not spend his sentence at a low security facility, after another spammer escaped from jail this weekend.