Common Knowledge in Email Exchanges

TL;DR

This paper models email communication among agents to analyze how information and common knowledge are formed, highlighting the unique epistemic effects of features like BCC that cannot be replicated by simpler message structures.

Contribution

It introduces a formal epistemic framework for email exchanges, including BCC, and demonstrates their distinct impact on agents' knowledge.

Findings

Agents learn from received emails about sent messages.

Common knowledge of email sending can be established.

BCC cannot be simulated by messages without BCC.

Abstract

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.