>Is it a privacy violation if someone checks a checksum of my incoming mail against a blacklist?
No, the privacy concern is about the potential for abuse if there is a known place in the world where a very detailed account of all my online (and some offline) activities, contacts, communication and personal interests is stored.
It obviously arouses the interest and desires of criminals, governments, employers, politicians, landlords, insurance companies, creditors, marketers, ex partners, extremists and bigots, journalists, potential mates, researchers, etc.
Some of these groups are overlapping and some of the concerns might only arise in the distant future. Governments change. Ownership of companies changes. Personal circumstances and opinions change, but you can't take anything back once its out.
Spam filters don't need to store all the contents. They can simply store hashes of contents.
So even if someone hacks into the spam filters, they won't be able to reconstruct content from your account. They _might_ have insight into things like word usage, but they won't have reconstructed sentences or the like, a priori.
You can build systems like this without having long-term storage of the content, which protects against data issues for one-time leaks.
No, the privacy concern is about the potential for abuse if there is a known place in the world where a very detailed account of all my online (and some offline) activities, contacts, communication and personal interests is stored.
It obviously arouses the interest and desires of criminals, governments, employers, politicians, landlords, insurance companies, creditors, marketers, ex partners, extremists and bigots, journalists, potential mates, researchers, etc.
Some of these groups are overlapping and some of the concerns might only arise in the distant future. Governments change. Ownership of companies changes. Personal circumstances and opinions change, but you can't take anything back once its out.