Virus Bulletin has posted the results of its latest round of anti-spam tests, with 18 of the 21 products tested as part of its May VB Spam report passing and able to claim certification.
The test pits products against a collection of spam messages, and grades them based on the ability to block spam while avoiding false positives on legitimate messages.
A final score is calculated by multiplying the false positive percentage by three and subtracting that number from the percentage of genuine spam blocked. To pass, the product must receive a final score higher than 96.
Virus Bulletin said that 17 of the 20 products that took the full test were able to meet the criteria.
An additional product, the Spamhaus ZEN plus DBL blacklist, was classified as a partial solution meant to be used alongside other products, and as such was tested and given certification in a separate category.
None of the three products that failed recorded false positive rates higher than two per cent or spam catching scores under 98 per cent.
Higher false positive rates appeared to prevent passing scores for MessageStream and modusGate, each of which caught more than 99 per cent of legitimate spam.
Sunbelt's Vipre offering blocked slightly less than 98.5 per cent of spam, with a false positive rate of less than one per cent to fall short of certification.
Among the products placed the highest on the VBSpam quadrant ranking system were Microsoft Forefront, Libra Esva, Sophos, BitDefender and Symantec Brightmail.