As spam levels continue to rise at unprecedented rates, antispam vendors have increased their efforts to offer ways to recognize and filter out, quarantine, or mark unsolicited e-mail as a potential problem.
Citation:
Neal Leavitt, "Vendors Fight Spam's Sudden Rise," Computer, vol. 40, no. 3, pp. 16-19, Mar. 2007, doi:10.1109/MC.2007.109