Spamhaus and subscription bombing

Spamhaus released a blog post today discussing the recent subscription bombing: Subscription bombing COI captcha and the next generation of mail bombs.
As I mentioned in my initial posts, this abusive behavior goes beyond spamming. This is using email to harass individuals. Spamhaus even mentions a potential service that can be used to do these kinds of mailbombing.
Things folks need to know is that this is not just about ESPs and commercial mail. One of the big targets was WordPress admin forms. As Spamhaus says:

[T]he onus of stopping this kind of attack is not only on ESPs or mailing list owners. It is on everyone that has any sort of web-based signup that results in an email being sent: somebody clearly spent a great deal of time assembling URLs of mailing lists, and of account sign up pages, and has written a script to submit addresses to them at speed. We suspect that this was a test run for a tool that will will soon be offered for sale in the ‘Underground Economy’: Mail-bombing as a Service – MaaS.

With more and more abuse happening, every one who runs a service online needs to be cognizant of the abuse potential. Moreover even paths that have been around and haven’t been exploited may be exploited in the future.
We need to protect ourselves by making services that are difficult, if not impossible, to use as abuse vectors.