Palo Alto, Calif.--Spam costs corporations an average of $49 per user per mailbox, and if a company ignores spam, that cost per user mailbox will increase to $257 in 2007, according to a newly released study by Radicati Group Inc. Worldwide financial losses due to spam will reach $20.5 billion this year and will mushroom to $198.7 billion by 2007, according to the study. False positives are among the most important spam issues for corporations. Seventy-five percent of respondents said having low false-positive rates is the No. 1 priority. The market for anti-spam solutions is expected to hit $653 million this year and grow to $2.4 billion by 2007.