Outlook MSG to RFC 822 Email Converter
Converting Microsoft Outlook MSG items into standard RFC 822 EML files allows proprietary desktop mail data to open in any open-source mail client or web reader.
Format Comparison & Technical Specifications
| Specification | MSG | EML |
|---|---|---|
| MIME Type | application/vnd.ms-outlook | message/rfc822 |
| Type | Microsoft Outlook item file | standard email message file |
| Compression | uncompressed OLE compound storage streams | none (MIME multipart encoded) |
| Standard Specification | Microsoft MS-OXMSG Specification | IETF RFC 5322 |
| Magic Bytes Header | D0 CF 11 E0 A1 B1 1A E1 (Compound File Binary OLE2 header) | From: / Received: / Return-Path: (RFC 822/5322 header lines) |
Format Overview & Applications
Microsoft Outlook saves individual dragged-and-dropped messages using the proprietary MSG format. This format relies on an OLE Structured Storage architecture, which locks the message content inside a binary container tied closely to Windows software. When users switch to cross-platform mail clients like Thunderbird, Apple Mail, or web-based tools, these proprietary files fail to open natively. Transforming MSG to EML bridges this gap. Professionals, system administrators, and digital archivists frequently convert these files during mailbox migrations or legal discovery projects. EML is a plain-text format that standardizes headers, body text, and attachments into a universal structure. This ensures long-term data preservation without depending on a single vendor's software ecosystem.
Technical Specifications & Codec Breakdown
The source MSG format uses the application/vnd.ms-outlook MIME type and is built on an OLE compound file structure, identifiable by the magic byte header hex signature D0 CF 11 E0 A1 B1 1A E1. This structure uses uncompressed binary storage streams to hold message properties, recipients, and attachments. In contrast, the destination EML format uses the message/rfc822 MIME type and has no compression. EML stores everything as a flat text file using standard MIME multipart encoding. Headers appear as plain ASCII text lines at the top, followed by boundaries separating the text body and binary attachments encoded in Base64.
OS & Browser Compatibility
Operating systems like Windows 10/11, macOS, and Linux support EML files natively through various desktop mail clients. Web browsers cannot open EML or MSG files directly without a viewer extension or webmail import tool. Mobile operating systems such as iOS and Android open EML files through native mail applications when handled as attachments, while MSG files require specialized third-party document viewers.
💡 Useful info
Keep original MSG backups in a secure archive before performing batch conversions, as some deeply nested OLE object streams or custom Outlook form properties may require specialized parsing to map completely into standard EML headers.
Format Comparison & Technical Specifications
A typical 5 MB business email containing high-resolution image attachments transfers in under 0.1 seconds on a 1 Gbps Fiber connection, roughly 0.5 seconds on a stable 5G mobile network, and about 2 seconds on an average 4G LTE connection.
Frequently Asked Questions
How do you convert Outlook MSG to RFC 822 Email without losing quality?
The conversion is completely lossless regarding message text, metadata, and file attachments. Because EML stores raw text and uses standard Base64 encoding for attachments, no data is compressed away or degraded during the structural translation from OLE streams to plain text.
What is the difference between Outlook MSG and RFC 822 Email?
MSG is a proprietary binary container using OLE compound storage streams designed specifically for Microsoft Outlook. EML is an open standard defined by RFC 822, storing email data as a plain-text file with clear header fields and MIME boundaries that any standard text editor or mail client can read.