Open RPMSG File

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E-mail File Formats


MSG is an e-mail file format used by Microsoft Outlook and based on Compound File Binary Format. MSG file format stores information in binary format including content, attachments and e-mail header information like recipients, date and content type. MSG files could be opened by many e-mail clients including Microsoft Outlook and Microsoft Outlook Express.


RPMSG is based on MSG file format and extended to support DRM protection. When e-mail client receives e-mails in RPMSG file format it needs to contact a DRM server to get restrictions associated with RPMSG file in order to know if e-mail could be opened or forwarded to a certain recipient. If e-mail client doesn’t support DRM or doesn’t have a connection to DRM server then e-mail from RPMSG file will not open.


EML files store e-mails in Internet Message File Format. EML files are plain text and could be easily imported to many e-mail clients including Microsoft Outlook, Microsoft Outlook Express, Mozilla Thunderbird. Also, it is possible to open EML files in internet browsers after changing file extension to MHT.


MBOX is an older file format used to store multiple e-mails in a single file. It also supports storing e-mails in a separate folder. There are multiple available MBOX file formats like mboxo, mboxrd, mboxcl, and mboxcl2. Microsoft Outlook Express, Apple Mail and Microsoft Outlook support importing from MBOX file format. Also, there are multiple free and paid tools on the market which are capable of MBOX conversion.


PST file format is used by Microsoft Outlook to store archived e-mail folders. PST files support compression which makes them effective when storing large number of e-mails in multiple folders. PST files are frequently used for e-mail backup purposes. OST file extension is similar to PST but used to store off-line e-mail files.

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RPMSG Quick Info
  Rights-Managed Email Object Protocol File
Opens with
  Microsoft Outlook
  Microsoft Outlook Web App (OWA)
  Azure Information Protection viewer