> but that everyone knows everyone else heard it.

How about simply having a company policy that everyone should MVCC their decisions based on received email "transactions"? I.e., if someone sends out an email, then everyone else MUST (in the RFC sense of MUST) read it and digest it before making any new decisions. It still operates asynchronously--you can finish whatever you were head-down working on before checking your email--but you have to check it before you move on to whatever comes after that.

Or, in more cynical terms: fire everyone who ignores these emails until the problem corrects itself.