The report tracked the ways that spam is determined which is mainly by blacklists and limiting inbound mail volume.

Network based filtering as well as content based are the primary detection methods employed by companies to cut down on spam.

Once the spam is found, the measures to prevent follow up are often time consuming and sometimes cause good emails from being received. The spam is traced back to the ISP and most times they are contacted regarding spam being sent from their servers. Banning IP addresses is another tactic used by many companies to stop spam messages.

The report detailed one critical issue with regards to spam blacklists. Many of the respondents reported that their own companys servers were added to the blacklists but not removed when the problem was corrected. This put a shadow on the reliability of the lists.

The full report from the ENISA can be found here:

http://www.enisa.europa.eu/act/res/other-areas/anti-spam-measures/studie...