What Is an MSG File? The Plain-Language Explanation
If someone sent you an MSG file and you can’t open it, you’re dealing with one of Microsoft Outlook’s more frustrating legacies. The format has been around for decades, it’s deeply embedded in corporate email workflows, and it’s almost completely useless outside of Outlook without the right tools.
Here’s what MSG files actually are, what’s inside them, and what you can do with them.
The Short Version
An MSG file is a saved email. When you save an email directly from Microsoft Outlook to your hard drive, it gets saved as an .msg file. It contains everything from that email: the sender, recipients, subject line, timestamps, body content, attachments, and a pile of metadata that most users never need to think about.
The problem is that MSG is a proprietary format created by Microsoft. It uses a binary storage system called Compound Document File Format — the same underlying technology used by older Office files like .doc and .xls. Opening it without Outlook or a compatible viewer requires a tool that knows how to parse that binary structure.
What’s Actually Inside an MSG File
If you could crack one open (which you can, with the right tools), you’d find:
- Message properties: Sender email, display name, all recipients, timestamps for send and receipt, message priority flags
- Subject line: Stored as a separate property, not just embedded in the body
- Body content: The email body is often stored in multiple formats simultaneously — plain text, RTF (Rich Text Format), and HTML — so Outlook can render whichever version is appropriate
- Attachments: Embedded as sub-objects within the same file, including their original filenames and content types
- Embedded images: Inline images from the email body are stored separately and referenced from the HTML body
- Extended MAPI properties: A large set of metadata properties covering everything from read/unread status to custom organizational fields
All of this gets packed into a single .msg file. That’s why the files can be surprisingly large even for emails with small text bodies — they carry a lot of metadata weight.
Why MSG Files Are Difficult to Work With
Three reasons MSG files cause friction:
1. The format is proprietary and undocumented (mostly). Microsoft eventually published partial documentation for the MSG format through their Open Specifications program, but for years it was entirely proprietary. The parsing libraries that exist today were largely reverse-engineered. This is why general-purpose converters often struggle with MSG files — they’re handling a format that was never designed to be portable.
2. There’s no native support outside Microsoft’s ecosystem. Windows doesn’t have a default viewer for MSG files. macOS doesn’t handle them. Linux doesn’t have native support. Gmail can’t open them. If you double-click an MSG file on a non-Windows machine without Outlook, you’ll get nothing — or an error telling you there’s no program associated with this file type.
3. The binary structure makes corruption risks higher. Unlike plain text formats that can be partially read even when damaged, MSG files are binary. A partially corrupted MSG file is often completely unreadable.
MSG vs. EML: EML is the open-standard alternative to MSG. Gmail, Apple Mail, Thunderbird, and most non-Microsoft email clients use EML. It’s a plain text format, which makes it far more portable. If you’re dealing with both file types, the MSG vs. EML breakdown covers the key differences and why they matter for conversion.
Common Situations Where You End Up With MSG Files
You probably didn’t go looking for MSG files — they landed in your lap. The most common scenarios:
- Legal holds and discovery requests: When lawyers or compliance teams request email records, many Outlook-based organizations export as MSG files because it’s the default. Recipients who don’t use Outlook suddenly have hundreds of unreadable files.
- IT migrations: Moving from Exchange/Outlook to Gmail or another platform sometimes results in MSG exports as part of the archive.
- Forwarded attachments: Someone dragged an email into a folder and sent the MSG file instead of forwarding the actual email.
- PST extractions: When extracting individual emails from a large Outlook PST archive, the individual emails come out as MSG files.
- Client deliverables: Some industries still send emails as attachments to other emails, particularly in legal, financial, and construction sectors.
How to Open an MSG File
Your options, ranked by ease:
Option 1: Convert it to PDF. This is usually the right call for anyone who just needs to read the content and doesn’t need to reply or edit. Converting to PDF gives you a readable, shareable, archivable version with all the original formatting intact. The step-by-step conversion guide walks through the process. The Outlook MSG to PDF page covers the specifics for Outlook-exported files.
Option 2: Use Microsoft Outlook. The obvious path if you have it. Open Outlook, drag the MSG file in, done. No conversion required, full fidelity. Not useful if you don’t have Outlook.
Option 3: Use a free MSG viewer. Several lightweight desktop tools can open MSG files without a full Outlook installation. Quality varies significantly. Most show the body content correctly but handle attachments inconsistently.
Option 4: Use a web-based tool. Browser-based MSG viewers and converters handle the parsing without requiring any installed software. For reading only, this is convenient. For conversion, it’s both convenient and gives you a portable output format.
What Happens When You Convert MSG to PDF
A properly built converter reads the binary structure of the MSG file, extracts the relevant properties, and renders them into a PDF layout. The output should include:
- Header block: From, To, CC, BCC, Date, Subject
- Body content with preserved formatting
- Embedded images from the body
- Attachment list (filenames and sizes)
- Thread history if the MSG includes quoted replies
The quality of the conversion depends heavily on how well the tool handles the binary parsing. Generic converters that treat MSG as an afterthought tend to produce flattened, formatting-stripped output. Purpose-built tools produce PDFs that actually look like the original email.
What About Bulk Conversion?
If you have a lot of MSG files — an archive from a litigation hold, an exported inbox, a set of client communications — converting them one at a time is impractical. The bulk MSG to PDF converter handles multi-file uploads and processes them as a batch. You’ll need a free account to access batch mode.
MSG Files in Legal and Compliance Contexts
One reason people end up researching MSG files in detail: they’ve received them as part of a legal discovery process. In that context, the completeness of the conversion matters. A PDF that drops the BCC field or strips timestamp metadata isn’t an accurate representation of the original email. The guide on MSG to PDF for legal eDiscovery covers what completeness looks like in a compliance-ready PDF.
Frequently Asked Questions About MSG Files
Can I convert MSG to Word instead of PDF? Technically yes, but PDF is almost always the better choice for preservation. PDF format doesn’t depend on any application to render correctly, and it’s widely accepted by courts, regulators, and clients as an archival format.
Will converting lose any data? A purpose-built converter captures all the content visible in the original email. The one area where information is inherently limited: attachments are referenced in the PDF (filename and size listed) but aren’t embedded as their original file types within the PDF. The attachment files themselves are separate.
Can I convert MSG files on a Mac? Yes — browser-based tools work on Mac, Windows, and Linux. You don’t need any platform-specific software.
What’s the maximum file size for conversion? The MSG to PDF Converter handles files up to 10MB. Most individual email files are well under this. Check the FAQ page for more common questions, or the pricing page for account and usage details.
Have an MSG file you need to read or archive? Convert it to PDF in seconds — no Outlook, no software installation needed.Convert MSG to PDF Now →