EML files: what they are and how to open one

An .emlfile is one email saved exactly as mail servers send it: a block of header lines (who it is from and to, the subject, the date, the servers it passed through), a blank line, and then the body, with any attachments packed into the same file as text. The layout is the internet’s standard message format, defined in RFC 5322, with MIME (RFC 2045) for the HTML version of the body and the attachments (RFC 5322). Because it is the standard, Gmail and Apple Mail both save single messages in this format, and almost every mail program can read it.

You do not need a mail client to read one. The quickest way, on any device, is a viewer that runs in your browser.

The quickest way, on any device

1. Open the EML viewer in any current browser: Chrome, Edge, Safari or Firefox, on a computer or a phone.
2. Drop the .eml file on the page, or tap the box to choose it from your files.
3. Read the message, its headers and its attachments. Images the message would load from the internet stay blocked, so opening it does not tell the sender you have read it.

The file is read by code running in that tab. It is not sent to a server, because this site has none that accepts files, and its security policy stops the page from contacting any other site. How it works explains how to check that for yourself.

How to open an EML file on Windows

Microsoft documents three ways to open a saved .eml in the new Outlook for Windows (Microsoft Support):

• Drag and drop:open Outlook and File Explorer side by side, then drag the file onto Outlook’s reading pane.
• Open with: in File Explorer, right-click the file, choose Open with, then Outlook (new).
• Double-click: this works when Outlook is the default app for .eml files. If it opens in something else, change the default app for the file type in Windows settings.

Without Outlook, use the EML viewer in Edge or Chrome.

How to open an EML file on a Mac

Apple Mail is itself a source of .eml files: choosing File › Save As with the Raw Message Source format saves one message as an .eml, and dragging a message to the desktop does the same (Apple Support, Mail User Guide for Mac). To read a saved one without adding it to your mailbox, or on a Mac with no mail account set up, open it in the EML viewer in Safari.

Apple Mail also keeps its own copies of messages as .emlxfiles. That is the same message with a length line in front and a list of Mail’s flags after it, and the viewer opens those too.

How to open an EML file on an iPhone or iPad

1. Save the .eml to your device first, for example to the Files app.
2. Open the EML viewer in Safari, tap the drop box and choose the file from Files.

On a phone the viewer works through files one at a time, because Safari on iOS gives each tab less memory than a desktop browser does.

How to open an EML file on Android

1. Download the .emlto your phone, for example with your mail app’s option to download an attachment.
2. Open the EML viewer in Chrome, tap the drop box and pick the file.

EML files and Gmail or Outlook on the web

Gmail creates .eml files rather than opening them. Open a message, choose More, then Download message, and Gmail saves it as an EML file; Google notes that you need a desktop mail client to open the file it downloads. Forwarding a message with Forward as attachment attaches it as an .eml too (Gmail Help). If you have no desktop mail client, the EML viewer opens the downloaded file in the same browser.

Outlook on the web is different: Microsoft says you can drag and drop a saved .eml into it to open the message (Microsoft Support).

What is inside an EML file?

Open an .eml in a text editor and you can read it. A short message with an HTML body, a plain-text alternative and one inline image looks like this:

1. ① Received: each server that handled the message adds one of these at the top, so reading them bottom to top traces its route and timing. The header analyser lays them out in order.
2. ② Encoded words: headers may only contain plain ASCII, so anything else, like an accent, a dash or a non-Latin subject, is written as =?charset?B?…?= and decoded by whatever reads the file.
3. ③ Content-Type and boundary: a multipart message is split into parts by a boundary string that appears on a line of its own, after two dashes (RFC 2045).
4. ④ The bodies: multipart/alternative holds the same text twice, plain and HTML, and a mail client shows the best one it can.
5. ⑤ Inline images and attachments: binary files are encoded as base64 text. An image shown inside the HTML is referenced by its Content-ID through a cid: link (RFC 2392), which is why it travels with the message rather than being fetched from the web.

Is it safe to open an EML file?

The file itself cannot run anything, but its HTML can ask for images from the sender’s server, which tells them when and where it was opened, and its links can point somewhere other than they say. If you were not expecting the message, read it somewhere that does neither. The EML viewer removes scripts and forms, blocks every remote image and lists what it blocked, shows where each link really goes, and flags look-alike sender addresses and risky attachments.

Converting an EML file

• EML to PDF: a text PDF with the headers and an attachment index, in batches, or a print view that keeps the message’s layout and inline images for your browser to save as PDF.
• Attachment extractor: every attachment as a ZIP, with SHA-256 hashes and a manifest.
• Outlook’s own .msg format is explained on MSG files, and EML vs MSG compares the two.

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. IETF: RFC 5322: Internet Message Format
2. IETF: RFC 2045: MIME Part One, Format of Internet Message Bodies
3. IETF: RFC 2392: Content-ID and Message-ID Uniform Resource Locators
4. Microsoft Support: Open .eml, .msg, and .oft files in new Outlook and Outlook on the web
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