ISPs in many countries, including the United States, enjoy a legal status often known as "Common Carrier." Simply put, this absolves the ISP of responsibility if it assists in the transfer of illegal materials, such as copyrighted works or child pornography. The philosophy is that as long as the ISP simply moves data from one place to another -- not making any judgment or discrimination about whether to move one type of data or another -- the ISP should enjoy a "safe harbor."
From time to time, some wag gets the idea that email filtering of spam and viruses would cause ISPs to lose this legal protection. In other words, if an ISP chooses not to deliver a message because it's "spam," the ISP is discriminating based on the content or source, which may remove the safe harbor. When one thinks about it, this is complete nonsense, but stranger things have happened in various legal systems around the world.
This debate is happening again. Thanks to the good work done by MAAWG and others, ISPs are being encouraged to set up outbound spam filtering, to prevent virus-infected PCs sending spam from their networks and to encourage users to clean their infected machines by use of a walled garden. Naturally, some are expressing concern that such discrimination would count as another chink in their common carrier armor.
It's time for the FCC and similar regulators in other countries to step up and make it clear that such genuinely useful -- some would say essential -- discrimination would not affect an ISP's common carrier status.
... Richi Jennings, with thanks to Cloudmark's Kevin Soo Hoo