“Open” vs “close” system

In both Proposal 1 (P1) design and Proposal 2 (P2) we should decide whether it should be possible to send Email to any Email service, eg. gmail or to a few Email services, eg. riseup and systemli or several different companies.

In the “open” system there’s no solution to avoid spam. If the public keys are available and anyone can join the mixnet, spammers can also send encrypted spam. Also, services like Gmail will refuse to receive Email from other domains/services not using [SPF]. If the mixnet provider/service uses SPF, then it’s not possible to have sender anonymity (unlinkability).

In the “close” system, a malicious provider could also inject spam, but it’d be less likely, specially if the users have to authenticate to the providers, which is the case of Katzenpost .

Diagram with errors:

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