Not many people are aware of “.rpmsg” files. The file extension means “restricted-permission message”. They are used to deliver email messages between people and implement some controls applied at the recipient side. Such permissions are, by example, the right to forward or copy the original email. You may compare this to some kind of “DRM” (Digital Rights Management) for emails. RPMSG files are used inside a Microsoft ecosystem because they are created by users of Azure Information Protection, or Active Directory Rights Management Services[1]. The file is encrypted and only the recipient will be able to decrypt and open the message.
Article Link: Be careful with RPMSG files