Quick answer: The fastest method is to log into outlook.com with the email address the message was sent to. Outlook Web App is free and handles RPMSG files natively — no app installation required.

Method 1: Outlook Web App (OWA) — Recommended

Outlook Web App is Microsoft's free browser-based email client. It has full IRM support and can open RPMSG files transparently — and it's completely free for personal Microsoft accounts.

  1. Open a browser and go to outlook.live.com (personal) or your organization's webmail URL (work)
  2. Sign in with the exact email address the protected message was sent to — this is critical
  3. Find the original email in your inbox (not the .rpmsg attachment — the email itself)
  4. Outlook Web will display the protected content directly in your browser after verifying your identity with Microsoft's RMS servers

Why this works: Outlook Web App is a Microsoft product with full Rights Management integration. It authenticates with Microsoft's RMS servers on your behalf and decrypts the content in the browser.

If it doesn't work: You're probably not the intended recipient, or you're logged into a different account. Make sure the account you sign in with is the exact address the email was sent to.

Method 2: Microsoft OME Viewer (Works in Gmail)

If you received the email in Gmail, Apple Mail, or another email client, look for a "Read the message" button inside the email body (not the .rpmsg attachment).

  1. Open the original email in Gmail (or your email client)
  2. Look for a blue button or link that says "Read the message" or "Click here to read the message"
  3. Clicking this opens Microsoft's Office Message Encryption (OME) viewer in a new browser tab
  4. You'll be prompted to authenticate: either sign in with your Google/Microsoft account, or request a one-time passcode sent to your email
  5. After authentication, the protected content displays in your browser
Can't find the button? If the "Read the message" button is missing, the sender may have sent only the .rpmsg attachment without the standard OME wrapper. In this case, use Method 1 (Outlook Web App) or Method 3.

Method 3: Microsoft Outlook Desktop App

If you have access to a Windows or Mac computer with Microsoft Outlook installed:

  1. Open Microsoft Outlook — ensure you're signed in with the account that received the email
  2. Navigate to the original email in your inbox
  3. Double-click the message.rpmsg attachment
  4. Outlook will contact Microsoft's RMS servers to verify your permissions
  5. If authorized, the content will display within Outlook

If it still doesn't open: Check that your Outlook is connected to the internet, and that you're signed in with the correct Microsoft account. Old versions of Outlook (2013 or earlier) may not support modern AIP encryption.

Method 4: Outlook Mobile App (iPhone & Android)

The official Microsoft Outlook app on iOS and Android has full IRM support:

  1. Download Microsoft Outlook from the App Store (iPhone) or Google Play (Android)
  2. Open the app and sign in with the account that received the protected message
  3. Add the email account if it's not already there — Outlook supports Gmail, Yahoo, and other accounts
  4. Navigate to the original email in your inbox
  5. The Outlook app handles RPMSG decryption automatically when you're the authorized recipient

Method 5: Use Our RPMSG Viewer + Ask the Sender

If none of the above methods work, you're likely not the authorized recipient, or the IRM policy has expired. Here's what you can do:

  1. Analyze the file — use our free RPMSG viewer to parse the file and see what issuer domain and policy was applied. This helps you understand why you can't open it.
  2. Contact the sender — ask them to either re-send the email without IRM protection, or to update the permissions to include your account
  3. Check if you have the right account — the RPMSG file may have been sent to a different email address than the one you're trying. Our viewer may show the intended recipient email from the permission token.

Common Problems & Fixes

Error: "You don't have permission to open this file"

This means your account is not listed as an authorized recipient in the IRM policy. Only the original sender can fix this by modifying the policy. Contact the sender and ask them to add your email address to the allowed recipients.

Error: "Your IRM license has expired"

The sender set an expiry date on the protected message. You'll need to contact the sender to re-issue the protected content with a new or extended expiry date.

The .rpmsg file opens as gibberish in Notepad or other apps

RPMSG files are binary OLE/CFB container files — they are not text files. Opening them in Notepad or text editors will show garbage. You must use one of the Microsoft methods above, or our viewer to parse the structure.

The "Read the message" button is missing from the email in Gmail

This can happen if the email was only sent as a raw .rpmsg attachment without the OME wrapper message. Try Method 1 (Outlook Web App) — log in to the email account the message was originally sent to and look for the email there.