InboxUnpack

Outlook MSG files: what they are and how to open one without Outlook

A .msgfile is how Microsoft Outlook saves a single item to disk: usually an email, sometimes a meeting, contact or task. Microsoft’s specification calls it the Outlook Item File Format, a way of storing an Outlook message object with all of its properties in a file (Microsoft Open Specifications). It is not an email in the internet’s standard format, which is why the usual answer to “how do I open this?” is “in Outlook”.

You do not need Outlook. Everything the message holds is inside the file, so a reader that understands the format can show it on any device, in a browser.

Open a MSG file →Read it in your browser. Nothing is uploaded.Convert MSG to EML →A standard .eml that other mail programs open.Convert MSG to PDF →Text PDF in batches, or a print view with the formatting.

Why Mac Mail, iPhone and Gmail can’t open a .msg file

Mail on the Mac, Mail on the iPhone and Gmail all work with email in the internet’s standard message format, the one an .eml file holds: plain text headers and MIME parts (RFC 5322). Apple documents exactly two things Mail on the Mac can import: mailboxes exported from Mail, and files in mbox format (Apple Support, Mail User Guide for Mac). Gmail saves and forwards single messages as .eml files (Gmail Help).

A .msg is neither. Inside, it is a Microsoft Compound File, a small filesystem in one file, made of storages and streams: the message and each recipient and attachment are storages, and their Outlook properties are streams within them (Microsoft Open Specifications blog). Nothing in it is laid out the way an internet message is, so a program has to implement Outlook’s format specifically to read it. Renaming the file to .eml does not help; the bytes are still the same container.

Open a MSG file without Outlook, on any device

  1. Open the MSG viewer in Safari, Chrome, Edge or Firefox.
  2. Drop the .msg on the page, or tap the box to choose it.
  3. Read the body, recipients, dates and attachments. Save attachments one by one or as a ZIP, and open any email attached inside it as a message of its own.

The file is read in that tab and never uploaded. That matters more than usual for .msg files, which tend to be business correspondence someone has exported for a reason.

How to open a .msg file on a Mac

Use the MSG viewerin Safari, as above. If you want the message in Apple Mail’s own format instead, convert it with MSG to EML: .eml is the format Mail itself writes when you save a message with Raw Message Source (Apple Support, Mail User Guide for Mac). The conversion carries the body, inline images and attachments across, and keeps the original headers when the .msg stored them.

How to open a .msg file on an iPhone, iPad or Android phone

  1. Save the .msgto your device: to the Files app on an iPhone or iPad, or with your mail app’s download option on Android.
  2. Open the MSG viewer in Safari or Chrome, tap the drop box and choose the file.

A .msg attachment in Gmail

Download the attachment from the message, then open it in the MSG viewer in the same browser. To keep it somewhere Gmail-friendly, convert it to .eml with MSG to EML, the format Gmail itself uses for downloaded and forwarded messages (Gmail Help).

If you do have Outlook

Microsoft documents three ways to open a .msg in the new Outlook for Windows: drag the file onto the reading pane, right-click it in File Explorer and choose Open with › Outlook (new), or double-click it when Outlook is the default app for the file type. You can also drag and drop one into Outlook on the web. Microsoft notes that opening .msg files needs a qualifying Microsoft 365 subscription (Microsoft Support). Without one, the browser viewer above does the same job.

What is inside a .msg file?

Microsoft’s specification puts it simply: any property the Outlook item has is also in the file (Microsoft Open Specifications). In practice that means:

Subject, sender and recipients
Stored as Outlook properties, each recipient in a storage of its own. Senders inside a company's Exchange system are sometimes stored as a directory name rather than an email address.
The body
Up to three versions: plain text, HTML, and compressed RTF. Many Outlook messages keep their formatted body only as compressed RTF with the HTML wrapped inside it, which is why some readers show them as blank.
Attachments
Each in its own storage, with its file name and type. An attached email is stored as a complete message inside the attachment, and can contain attachments of its own.
The original internet headers
Only if Outlook kept them. Mail that was received usually has them; a message composed and saved, or copied from Sent Items, often has none, so there is no delivery route to inspect.
Outlook-only details
Categories, follow-up flags, importance and the item type. The same format also saves meetings, contacts and tasks.

The MSG viewer shows all of this, including a property inspector for the raw Outlook fields, and says plainly when a field was not in the file rather than filling the gap with a guess.

Converting a .msg file

  • MSG to EML: a standard message any mail client opens. Converting this way is a reconstruction, because the .msg holds properties rather than the original message; the result records which headers were original and which were rebuilt.
  • MSG to PDF: a text PDF with the headers and an attachment index, or a print view that keeps Outlook’s formatting and inline images.
  • Attachment extractor: every attachment out of one or many .msg files, as a ZIP with SHA-256 hashes.
  • EML vs MSGcompares the two formats side by side, and Outlook’s whole-mailbox .pst files are covered in how to open a PST file without Outlook.

Sources

Each platform step above comes from the vendor’s own documentation, listed here. Steps we could not find documented by the vendor are left out rather than written from memory.

  1. Microsoft Open Specifications: [MS-OXMSG]: Outlook Item (.msg) File Format, overview
  2. Microsoft Open Specifications blog: .MSG File Format (Part 1)
  3. IETF: RFC 5322: Internet Message Format
  4. Apple Support, Mail User Guide for Mac: Import or export mailboxes in Mail on Mac
  5. Apple Support, Mail User Guide for Mac: Save emails as files or PDFs in Mail on Mac
  6. Gmail Help: Download emails to your computer
  7. Microsoft Support: Open .eml, .msg, and .oft files in new Outlook and Outlook on the web