Common Knowledge in Email Exchanges

We consider a framework in which a group of agents communicates by means of emails, with the possibility of replies, forwards and blind carbon copies (BCC). We study the epistemic consequences of such email exchanges by introducing an appropriate epistemic language and semantics. This allows us to find out what agents learn from the emails they receive and to determine when a group of agents acquires common knowledge of the fact that an email was sent. We also show that in our framework from the epistemic point of view the BCC feature of emails cannot be simulated using messages without BCC recipients.