Privacy and security

[polarbirke]

We should look critically at the information we disclose in success/failure screens after form submissal as well as in sent e-mails. This package makes pretty good inroads into this, but the topic came up recently in https://github.com/webfactory/gemeinsamer-bundesausschuss/pull/714.

[MalteWunsch]

The specific point raised there was this (too revealing) message (and perhaps underlying mechanism).