[chrismorgan]

The vast majority of operations in these fields are mind-bogglingly simplistic.

Well-known rules will block most spam, some with occasional collateral damage but many with no realistic chance of collateral damage.

Entity-encoding @ as @ in email addresses in HTML will block the vast majority of email address harvesters, with no collateral damage.

Adding a honeypot field to an HTML form, with the label “If you are human, leave this field blank” and hidden by CSS, will catch practically all spam submissions, with no collateral damage.