File Extension GuideWhat is an EML File?
An EML file is a single email message saved as one file, with the .eml extension. It holds the whole message: the sender, the recipients, the subject, the date, the body and any attachments, all in one plain-text file you can open, save or send on.
EML follows the same internet message standard that real email uses, so the file is just the email written out to disk. Because the format is open and text-based, almost every email program reads it, including Mozilla Thunderbird, Windows Mail, Apple Mail and Microsoft Outlook. That wide support is why EML is a popular way to keep a copy of an important email or move messages between programs.
The key idea to remember is one email per file. If you have a hundred messages saved as EML, you have a hundred .eml files. This is different from formats like MBOX or PST that pack many emails into a single file.
Quick Facts
| File Extension | .eml (Apple Mail uses .emlx) |
| Full Name | Email Message |
| Category | Email Message File (single message) |
| MIME Type | message/rfc822 |
| Based On | RFC 5322 internet message format with MIME |
| Popularized By | Microsoft Outlook Express (1990s) |
| File Type | Plain text (readable headers and body) |
| Character Encoding | ASCII or UTF-8 with MIME encoding |
| Messages Per File | One (a single email) |
| Attachment Support | Yes, MIME encoded (Base64) |
| Typical Size | A few KB to several MB, depending on attachments |
History & Origins
The EML file did not appear out of nowhere. It is built on the same message format the internet has used for email since the early 1980s:
1982 - The Message Standard
RFC 822 set out how an internet email message is laid out, with headers like From, To, Subject and Date followed by the body. EML files follow this same layout.
1990s - The .eml Extension
Microsoft Outlook Express used the .eml extension to save single messages to disk. The name stuck and other programs began saving emails the same way.
2001 - RFC 2822
The message standard was updated and tidied up, keeping the same headers-then-body shape that EML uses.
2008 - RFC 5322
RFC 5322 became the current internet message standard. A modern .eml file is an RFC 5322 message saved as a file.
Today
EML is a universal single-message format. Thunderbird, Windows Mail, Apple Mail, Outlook and many other programs can open and create it.
EML File Structure
An EML file has a simple shape: a block of headers at the top, then a blank line, then the message body. Unlike MBOX, an EML file does not start with a "From " separator line, it begins right at the headers. Here is what a basic EML looks like inside:
To: Jane Doe <jane@example.com>
Subject: Meeting Tomorrow
Date: Mon, 20 Jan 2025 10:30:00 -0500
Message-ID: <abc123@mail.example.com>
MIME-Version: 1.0
Content-Type: text/plain; charset="UTF-8"
Hi Jane,
Just confirming our meeting tomorrow at 2 PM.
Best regards,
John
The Main Parts
Headers
The lines at the top, such as From, To, Subject and Date. They tell the email program who sent the message, who it was for and when. Each header is a name, a colon and a value.
Blank Line
One empty line marks the end of the headers and the start of the message. Everything after it is the body the reader sees.
Message Body
The text of the email. It can be plain text, HTML for a formatted look, or both, so the program can show whichever it supports.
Attachments (MIME)
Files are tucked inside the same EML using MIME encoding (usually Base64). This is why a single .eml file can carry its attachments with it.
Common Headers in an EML File
| Header | What It Means | Example |
|---|---|---|
From | Who sent the email | John Smith <john@example.com> |
To | Who the email was sent to | jane@example.com |
Subject | The subject line | Weekly Report |
Date | When it was sent | Mon, 20 Jan 2025 09:00:00 -0500 |
Message-ID | A unique id for the message | <abc123@mail.example.com> |
MIME-Version | Marks the message as MIME | 1.0 |
Content-Type | The kind of body and its charset | multipart/mixed; boundary="..." |
EML and EMLX
You may run into a few names that look similar. Here is how they relate so you do not mix them up:
The Standard
Works Everywhere
- One email per file
- Open, plain-text format
- Opens on Windows, Mac and Linux
- Used by most email programs
Apple Mail
Mac Version
- Used by Apple Mail on a Mac
- Still one message per file
- Adds a little extra Apple Mail data
- Close cousin of .eml
Not an EML
Outlook Format
- Microsoft Outlook's own format
- Single message, but binary
- Built for Outlook, not open text
- A different format, not a type of EML
How to Open an EML File
EML opens in plenty of free programs. Pick the one for your system:
Windows
macOS
Linux
Any System
Open an EML in Mozilla Thunderbird
- Install Thunderbird if you do not have it (free from mozilla.org).
- Open the file by double-clicking the .eml, or drag it into a Thunderbird folder.
- Read the message, the sender, subject, date and body all show as normal.
- Save attachments from the message if it has any.
Open an EML on Windows
- Double-click the .eml file. Windows Mail or your default email app opens it.
- If it opens in the wrong app, right-click the file, choose Open with and pick your email program.
- To just read the text, open the file in Notepad to see the headers and message.
How to Create or Save an EML File
Most email programs let you save a message as an EML file so you can keep or share it. The wording differs a little by program:
In Mozilla Thunderbird
- Open or select the email.
- Right-click it and choose Save As, or use the menu.
- Pick a folder and the EML file type.
- The message is saved as a .eml file.
In Microsoft Outlook
- Open the email you want to save.
- Drag it from Outlook onto your desktop or a folder.
- Outlook saves it as a .msg file by default. To get .eml, save through a webmail account or a converter.
- You can then keep or send the file.
Common Uses
EML files turn up in a lot of everyday email tasks:
Save a Single Email
Keep an important message as a file on your computer, separate from your mailbox, so it cannot be lost if the account changes.
Share Emails
Send a saved message to someone as a file. They can open the .eml in their own email program and see it exactly as it was.
Move Between Programs
Because almost every client reads EML, it is an easy way to move messages from one email program to another.
Legal and Evidence
One message per file makes EML handy for legal review and case work, where single emails are tagged and shared.
Long-term Archive
Store old messages as plain EML files that will still open years from now, with no special program needed.
Record Keeping
Save proof of orders, receipts and approvals as files you can file away and find later outside your inbox.
EML vs Other Formats
Knowing how EML compares to other email formats helps you pick the right one:
EML vs MSG
| Feature | EML | MSG |
|---|---|---|
| Format Type | Open, plain text | Microsoft binary |
| Made By | Internet standard (RFC 5322) | Microsoft (Outlook) |
| Opens In | Almost any email program | Mainly Outlook |
| Human Readable | Yes | No (binary) |
| Holds | One email and its attachments | One email, plus Outlook extras |
| Best For | Sharing and saving across programs | Staying inside Outlook |
EML vs MBOX
| Feature | EML | MBOX |
|---|---|---|
| Structure | One email per file | Many emails in one file |
| File Count | Many files (one per email) | A single file per folder |
| Computer Search | Works with file search | Needs an email program |
| Best For | Single emails, sharing | Whole-folder backup |
- You want to save or send single emails
- You need a file most programs can open
- You are tagging emails one by one
- You want plain, future-proof files
- You are backing up a whole folder
- You want one file instead of many
- You are moving to Thunderbird or Apple Mail
- You want Mac and Linux support
- You work mainly in Outlook
- You want to keep Outlook details
- You share files with Outlook users
- You do not need to open them elsewhere
Troubleshooting
Common problems with EML files and how to fix them:
- Set the default app: right-click the file, choose Open with and pick Thunderbird, Windows Mail or your email program.
- Check the extension: make sure the file ends in .eml and was not renamed to .txt.
- Try another program: if one client fails, open the same file in Thunderbird or Apple Mail.
- Use a text editor: EML is plain text, so Notepad will at least show the headers and message.
- Use a full email client: a text editor shows attachments only as encoded text, an email program decodes them.
- Incomplete file: a large attachment may have been cut off when the EML was saved, ask for the file again.
- Encoding problem: broken line breaks in the encoded part can stop an attachment opening, try another client.
- Wrong encoding: open the file with UTF-8 selected if your program lets you choose.
- Older messages: very old EML files may use an unusual character set, a modern client usually fixes the display.
- Check the header: the Content-Type line names the charset the message should use.
- Drag them in: select the .eml files and drag them into an Outlook folder.
- Convert in bulk: for many files, convert the EML set to PST first, then open the PST in Outlook.
- One at a time works too: double-click each file, then move it into the folder you want.
Frequently Asked Questions
Yes. EML is an open format, so many free programs open it:
- Mozilla Thunderbird: open the file or drag it into a folder.
- Windows Mail: double-click the .eml file on Windows.
- Apple Mail: open EML on a Mac.
- A text editor: since EML is plain text, Notepad or any editor shows the headers and message.
Outlook can read EML, it just has no bulk import button. The easy ways are:
- Drag and drop: drag one or more .eml files straight into an Outlook folder.
- Open then save: double-click the .eml file, then in Outlook use Save As or move it to a folder.
- For many files: a converter that turns EML into PST or imports it in bulk is faster than doing them one by one.
EML is an open, plain-text format based on the internet message standard, so it opens in almost any email program. MSG is Microsoft's own format for Outlook, saved as a binary file that is built for Outlook and not easy to read elsewhere. Choose EML when you want a file that works everywhere, and MSG when you stay inside Outlook and want to keep every Outlook detail.
EMLX is the version Apple Mail uses on a Mac. It holds a single message just like EML, with a little extra Apple Mail data added at the top and bottom. A plain .eml file is the standard form that works across Windows, Mac and Linux email programs.
To move EML into Outlook you usually convert it to PST. The simplest way is a dedicated EML converter that writes PST, PDF, MSG and more in one step. You can also drag the .eml files straight into Outlook, then export that Outlook folder to a PST file. A converter is the easiest choice when you have many files.
Because each EML is one message, you often want them in one place. You can import the whole folder of .eml files into Thunderbird or Apple Mail, which groups them together, or use a converter to roll them into a single PST or MBOX file. Keeping them in one folder also lets your computer's file search find them.
An EML file is plain text and cannot run on its own, so opening one to read it is low risk. The usual care still applies: an EML can carry an attachment, so do not open attachments from senders you do not trust, and scan anything you are unsure about. EML files are also not encrypted, so store private ones on a secure drive.
Related Tools
OST to EML Converter
Turn an Outlook OST mailbox into separate EML files, no Outlook needed.
Convert OST to EML →Summary: Key Points About EML Files
- An EML file is a single email saved as one file
- Uses the .eml extension (Apple Mail uses .emlx)
- Plain text format you can read in any editor
- Holds one email, with headers, body and attachments
- Built on the RFC 5322 internet message standard
- Opens in Thunderbird, Windows Mail, Apple Mail and Outlook
- Good for saving, sharing and archiving single emails
- MSG is Outlook's own format, not a type of EML
- MBOX holds many emails, EML holds one
- Read by nearly every email program on every system