What Is an EML File? The Format, Explained
An .eml file is a single email message saved in the internet's native mail format. Here's what's actually inside one, why the format is everywhere, and how it differs from .emlx and .msg. Want to just open yours? Use the free viewer — it runs entirely in your browser.
The format under the hood
EML is not a Microsoft invention or anyone's proprietary format — it's simply an email message as it travels between mail servers, written to disk. The structure comes from RFC 822 (1982, later updated as RFC 2822 and RFC 5322): a block of headers, one per line — From, To, Subject, Date, plus dozens of technical ones like Received and Message-ID — then a blank line, then the body.
Modern emails layer MIME (RFC 2045–2047) on top of that skeleton. MIME is what lets one text file carry rich content: the body is split into partsseparated by boundary markers — typically a plain-text version and an HTML version of the same message, plus one part per attachment. Binary attachments are encoded as base64 text; accented and non-Latin text uses encodings like quoted-printable; subject lines in other languages use RFC 2047 "encoded words". That's why an .eml opened in Notepad shows readable headers followed by walls of seemingly random letters — it's all real data, just encoded for safe text transport.
The payoff of this design: EML is durable and universal. A message saved in 1995 still opens today, and every serious mail tool — plus this site's viewer — can parse it.
What's inside a typical .eml
From, To, Cc, Subject, Date — plus the Received chain (every server the message passed through), Message-ID, and authentication results (SPF/DKIM/DMARC). Gold for verifying where an email really came from.
The plain-text version of the message. Nearly every email includes one alongside the HTML.
The formatted version — fonts, colors, layout tables, images. What your mail app actually displays.
Images embedded in the design, referenced by cid: identifiers and carried as base64 parts inside the same file.
Any files attached to the email, base64-encoded with their filename and MIME type — PDFs, spreadsheets, even other .eml messages.
EML vs EMLX vs MSG
The open standard described above. Made by Gmail, Outlook, Thunderbird, Apple Mail exports and most servers. Text-based, portable, ageless.
Apple Mail's internal storage variant: an .eml wrapped with a byte-count line at the top and an XML property list at the bottom. Same message inside — our viewer unwraps it automatically.
Outlook's proprietary binary format (OLE compound file). Not text, not portable, needs a dedicated parser. See our MSG viewer page for the full story.
How to open an EML file
Desktop mail clients (Thunderbird, Apple Mail, desktop Outlook) open .eml natively. Without one, the quickest route on any device is a browser-based viewer: drop the file on our homepage and it renders instantly, with nothing uploaded. For platform-specific walkthroughs — Chrome, Gmail, Outlook on the web, Mac, iPhone — see How to Open an EML File.
FAQ
What is an EML file in simple terms?
It's one email, saved as a file. The .eml extension marks a message stored in the internet's standard email format (MIME/RFC 822): the headers (From, To, Subject, Date), the message body, and any attachments encoded as text — all in a single portable file.
What program creates EML files?
Almost every mail system: Gmail's 'Download message' produces one, Outlook and Thunderbird save messages as .eml, Apple Mail exports them, and mail servers pass them around internally. If you've ever saved or been forwarded 'an email as a file', it was almost certainly an .eml.
Is it safe to open an EML file?
The file itself is just text, but its HTML body can contain tracking images and its attachments can contain anything an email can carry — so treat unknown .eml files with the same caution as unknown emails. Our viewer renders the body in a sandboxed frame with scripts stripped and disabled, which makes inspecting a suspicious file much safer than opening it in a live mail client.
Can I open an EML file in Word or Notepad?
Notepad will open it — as raw MIME source: readable headers followed by walls of base64 text for the HTML body and attachments. Word does no better. To see the email as an email, use a mail client or drop the file into our free viewer.
EML vs MSG — which one do I have?
Check the extension. .eml is the open standard, text underneath, made by most mail apps; .msg is Outlook's proprietary binary format, made when you drag a message out of Outlook for Windows. Our viewer opens both.