Open RPMSG File

Message.rpmsg

The RPMSG file format is used for delivering e-mails with the Rights-Managed Email Object Protocol enabled. This protocol controls e-mail access and usage permissions. Instead of plain text, e-mails via RPMSG files are sent with content encrypted and stored as an encrypted file attachment. The RPMSG format is used to send e-mails with rights management information attached, allowing users to specify certain restrictions to an e-mail, such as disabling forwarding, restricting e-mail access rights only to specific users, restricting printing, and copying. Permissions to rights-restricted e-mails are enforced independently from the device where the e-mail is received because rights management information is encoded in the e-mail itself.

Message.rpmsg as an Email Attachment

If you encounter a file with the extension "message.rpmsg" as an email attachment, it is not a protected document but a protected email message that displays as an attachment. You cannot use the Azure Information Protection viewer for Windows to view this protected email message on your Windows PC. Instead, you need an email application for Windows that supports Rights Management protection, such as Office Outlook, or you can use Outlook on the web. However, if you have an iOS or Android device, you can use the Azure Information Protection app to open these protected email messages. You can download this app for these mobile devices from the Microsoft website.

Authentication for Protected Files

Before you can view the protected file, the Rights Management service that was used to protect the file must first confirm that you are authorized to view the file. The service does this confirmation by checking your user name and password. In some cases, these credentials might be cached, and you do not see a prompt that asks you to sign in. In other cases, you are prompted to supply your credentials.

If your organization does not have a cloud-based account for you to use (for Microsoft 365 or Azure) and does not use an equivalent on-premises version (AD RMS), you have two options:

1. If you were sent a protected email, follow the instructions to sign in with your social identity provider (such as Google for a Gmail account) or apply for a one-time passcode.
2. You can apply for a free account that will accept your credentials so that you can open documents that are protected by Rights Management. To apply for this account, click the link to apply for RMS for individuals and use your company email address rather than a personal email address.

Other Versions of RPMSG Files

As for the other versions of RPMSG files (message_v2.rpmsg, message_v3.rpsmg, and message_v4.rpmsg), they could be either corresponding versions of the RPMSG protocol or just copies of the original message.rpmsg file with versioning info attached.

For more information refer to View messages sent with restricted permissions in Outlook for Windows article.