Junk e-mail is costing businesses in the UK £1.3bn a year in lost productivity, IT costs and helpdesk charges - equivalent to £22 per user per year, research has revealed.
Analyst firm Ferris Research found that UK firms receive more spam than businesses in France, Germany, Italy and China.
It calculated that spam filtering software could have a return on investment of between 30% and 220%, or higher for companies that receive large volumes of junk e-mail.
But Ferris warned that IT suppliers' claims about the effectiveness of spam filtering software can be exaggerated.
Leading IT suppliers claim their software is capable of removing 95% or more of spam automatically, with false positive rates of three legitimate messages filtered out as spam for every 100,000 incoming messages.
But in practice, false positive rates can be much higher, ranging from 0.01% (equivalent to one false positive every 20 weeks) and 1% (equivalent to five false positives a week).
Leaving staff to control their own junk e-mail costs an average of £374 per user per year, Ferris said.