Guide
How to open an EML file
An .eml file is a plain-text email export — the format Outlook, Apple Mail, Thunderbird and most webmail “export message” buttons produce. On Windows and macOS it usually opens automatically in whichever mail app is set as default; if you don’t have one installed, or don’t want to import it into your inbox, a browser-based EML viewer opens it without touching your mail account.
What’s actually inside an .eml file
An EML file is a single text file containing:
- Headers — From, To, Subject, Date, and routing information added by each mail server the message passed through.
- Body — the plain-text and/or HTML version of the message.
- Attachments — encoded inline as Base64 text, inside the same file.
Because it’s plain text, you can technically open an .eml file in Notepad — you’ll see the raw headers and a wall of encoded text, which is why a proper viewer matters.
Opening .eml in specific apps
| App | How to open |
|---|---|
| Outlook (Windows desktop) | Double-click the file, or drag it into a folder to import it |
| Outlook (new Outlook / web) | Drag-and-drop isn’t supported the same way; use File → Open or a viewer instead |
| Apple Mail | Double-click opens it directly in Mail |
| Thunderbird | Requires the ImportExportTools NG add-on to open standalone .eml files |
| Windows Mail | Often has no default handler; Windows may ask you to pick an app |
Opening it without installing anything
If you’d rather not import a stray file into your mail account — or you’re on a machine without a mail client at all — a browser-based viewer reads the file locally and shows you the headers, body and attachment list without uploading it anywhere.
Known limitations
Very large attachments (embedded videos, multi-gigabyte files) can be slow to render in any browser-based tool, since everything happens on your device rather than a server. Encrypted (S/MIME) messages will show headers correctly but can’t display the body without the recipient’s private key.