What an RPMSG file is and why you might have one

An RPMSG file is a restricted permission message — a file format created by Microsoft Outlook that contains an email message with encryption and usage restrictions built in. When someone sends you an RPMSG file instead of a regular email, it means the sender applied Information Rights Management (IRM) protection, which limits what you can do with the message: you might not be able to forward it, print it, copy text from it, or save it to your computer.

You'll typically receive an RPMSG file as an attachment when a sender uses Outlook's "Restrict Permission" feature or when their organization has set up automatic encryption for certain types of messages. The file itself is usually small — just a few kilobytes — because it's really just the message container, not the full email with all its attachments.

The main reason people send RPMSG files is to protect sensitive information like financial data, legal documents, or confidential business details. The restrictions are enforced by your computer or device, not by a server, so you need the right software to read and respect those restrictions.

Key Takeaways

  • RPMSG files open in Microsoft Outlook on Windows or Mac, or in Outlook on the web if your organization uses Microsoft 365.
  • You cannot open an RPMSG file in Gmail, Apple Mail, Thunderbird, or other third-party email clients — the format is proprietary to Outlook.
  • If you don't have Outlook, you can view the message through Outlook on the web by signing into your Microsoft account, provided your organization has set that up.
  • The restrictions on the file (no forwarding, no printing, no copying) are enforced by your device and cannot be removed without the sender's permission.

Opening an RPMSG file in Outlook on Windows

If you have Microsoft Outlook installed on your Windows computer, opening an RPMSG file is straightforward. Double-click the RPMSG file from your Downloads folder or wherever it was saved. Outlook will launch automatically and display the message in a new window, showing you the sender, subject line, and body text.

The first time you open an RPMSG file, Windows may ask you to confirm that you want to open it with Outlook. Click "Open" or "Yes" to proceed. After that, RPMSG files will open directly in Outlook without the confirmation step.

Once the message is open, you'll see a banner at the top or bottom of the message indicating that it has restricted permissions. This banner will tell you what you cannot do — for example, "This message cannot be forwarded" or "Printing is not allowed." The exact restrictions depend on what the sender chose when they protected the message.

Opening an RPMSG file in Outlook on Mac

On a Mac, the process is similar but Outlook for Mac has some limitations with RPMSG files. Double-click the RPMSG file, and it should open in Outlook. However, Outlook for Mac does not fully support all IRM features, so you may see a message saying the file cannot be opened or that you need to use a different version of Outlook.

If Outlook for Mac won't open the file, your best option is to use Outlook on the web instead. Sign into your Microsoft 365 account through a web browser, navigate to your inbox, and ask the sender to resend the message as a regular email or through a different method. Alternatively, if your organization uses Microsoft 365, you can ask your IT department whether they can convert the file to a format that works on Mac.

Accessing RPMSG files through Outlook on the web

If you don't have Outlook installed, or if you're using a device that Outlook doesn't support well, you can open RPMSG files through Outlook on the web. Go to outlook.office.com or outlook.live.com (depending on whether you use a work or personal Microsoft account), sign in, and look for the RPMSG file in your inbox or attachments.

Outlook on the web will display the message directly in your browser without requiring you to download or install anything. The restricted permissions will still apply — you won't be able to forward, print, or copy the message if those restrictions are in place — but you can read it and respond to it if the sender allowed replies.

This method works on any device with a web browser, including phones and tablets, as long as you have internet access and a Microsoft account. However, some organizations restrict access to Outlook on the web, so this option may not be available to you depending on your workplace setup.

What to do if you cannot open the file

If you've tried opening the RPMSG file and it won't open, the most common reasons are: you don't have Outlook installed, your version of Outlook is outdated, or your device doesn't have the right permissions to read encrypted files. Start by checking whether you have Outlook installed. If you don't, install it from Microsoft's website or through your organization's software portal.

If you do have Outlook, make sure it's up to date. Open Outlook, go to File > Office Account (or Outlook > About Outlook on Mac), and check for updates. Install any available updates and restart Outlook, then try opening the RPMSG file again.

If the file still won't open, contact the person who sent it to you. Ask them to resend the message as a regular email, or ask whether they can remove the restrictions. They may also be able to tell you whether there's a specific version of Outlook you need, or whether your organization has special requirements for opening protected messages.

Understanding the restrictions on RPMSG files

When you open an RPMSG file, you may see restrictions that prevent you from forwarding the message, printing it, copying text, or saving it to your computer. These restrictions are not a bug or a security measure on your device — they're intentional protections that the sender put in place to keep the information from spreading beyond the intended recipient.

The restrictions are enforced by your operating system and Outlook working together, not by a remote server. This means the sender cannot revoke the restrictions after sending the message, and you cannot remove them yourself. If you need to forward the message or print it, you have to ask the sender to resend it without restrictions, or to give you permission to do those things.

Some RPMSG files allow you to reply to the sender but not forward to others. Others allow you to read the message but not copy any text. The specific restrictions vary depending on what the sender chose, and you'll see them listed in the banner at the top of the message.

Alternatives if you cannot use Outlook

If you don't have access to Outlook and cannot use Outlook on the web, your options are limited. RPMSG is a proprietary Microsoft format, and no other email client — Gmail, Apple Mail, Thunderbird, or others — can open it. There is no universal converter or tool that can transform an RPMSG file into a format that other email clients can read.

Your best path forward is to contact the sender and ask them to resend the message in a different format. They could send it as a regular email, paste the content into a Word document and encrypt that instead, or use a different secure messaging system that your email client supports. If the sender is part of your organization, your IT department may also be able to help you access the message through a different method.

Frequently Asked Questions

Can I open an RPMSG file on my phone?

Yes, if you use Outlook for iOS or Outlook for Android. Download the app from the App Store or Google Play, sign in with your Microsoft account, and the RPMSG file should appear in your inbox. You can read it on your phone, but the same restrictions (no forwarding, no printing, no copying) will still apply.

What does it mean if the RPMSG file says "This message cannot be forwarded"?

The sender chose to restrict forwarding when they protected the message. You can read it and reply to the sender, but you cannot send it to anyone else. If you need to share the information with someone else, ask the sender for permission or ask them to send the message directly to that person instead.

Can I convert an RPMSG file to a PDF or Word document?

Not directly. If the RPMSG file allows printing, you can print it to a PDF file using your computer's print-to-PDF feature. If printing is blocked, you cannot convert it without the sender's permission. Ask the sender to remove the restrictions or to send you the information in a different format.

Why did I receive an RPMSG file instead of a regular email?

The sender used Outlook's "Restrict Permission" feature, or their organization has automatic encryption turned on for certain types of messages. This is usually done to protect sensitive information. If you're unsure why the message was restricted, you can reply to the sender and ask them.

Is an RPMSG file a virus or malware?

No. RPMSG is a standard Microsoft file format used for encrypted email. However, like any file, it could theoretically contain malware if it came from an untrusted source. If you don't recognize the sender or weren't expecting the message, it's safe to ask the sender to confirm they sent it before opening it.