Our service would be to provide an I am not spamming commitment. A flag that can be put in a message which signals "This is the only flagged message I have sent this week"
Where will your credibility come from?
Alice receives a message from Bob. It says "You're amazing, we're nothing but mammals, let's do it like they do on the Discovery Channel", and it also says "I, Mallory, hereby certify that Bob only talked about mammals once this week -- to you".
Why should Alice believe you?
Things like that are technically possible (e.g. cryptographic proofs-of-work) but Alice is unlikely to verify your proofs herself and why should she trust Mallory, anyway?
I think if we had a nice professional website, with a link to a long description of how it all works that people won't read anyway, they will tend to trust us.
Especially if we use math.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.