Perhaps the largest ISP in Hong Kong has introduced a policy to control the number of recipients per mail and rate limit the number of mails send from each mail server within a minute. Why?
The obvious answer is to reduce spam, but a moment’s thought reveals that these measures are ineffective against the worst spammers, who are using illegally gathered botnets. Those spammers can easily split the spam to the ISP over thousands of zombies, so the rate limit and recipients per mail limit are never exceeded.
Conversely, the policy is disruptive to organisations with legitimate mailing lists using a single server who are trying to be efficient in the use of resources. Although bandwidth is now a lot more abundant than when SMTP was designed, transferring a message once for delivery to all the recipients at a site obviously reduces traffic.
Spam is slowly killing email; do we need the policies of shortsighted ISPs to make things worse?