(Matthew Broersma, ZDNet UK) Less than five percent of all email is delivered to mailboxes, as the rest is junk blocked by spam-fighting efforts, according to Enisa, the European Network and Information Security Agency.

While anti-spam measures are well used by providers, junk email remains a key problem for them and takes up a large part of their annual budgets, according to the report. [...] One-quarter of very small providers said they spent more than €10,000 (£8,700) per year on fighting spam, and one-third of very large providers invested more than €1m per year.

"The data on aborted SMTP connections and filtered emails seems to show that anti-spam measures are currently highly effective," study says. The result is that only 4.4% of all email was delivered, down from 6% in Enisa's last spam report 2 years ago.

The agency noted that many providers, though not all, currently use collaborative measures to fight junk mail, such as working with spam-sending ISPs to eliminate the problem. It recommended that more service providers should work together on the problem.