EML File: What It Is, How to Open One, and How to Convert It

Quick answer: An EML file is a single email message saved to disk as plain text in the MIME format defined by RFC 5322. It holds the message headers, the body, and any attachments encoded as text, exactly as the email traveled across the internet. Because EML is an open standard rather than a vendor format, almost any mail client can open it, and any text editor will show you its raw contents.

Most people meet the EML file type by accident. You export a mailbox, a colleague sends you an archive, a compliance request lands on your desk, or a system dumps a few thousand messages into a directory. You double-click one and something either opens or nothing does. Below is what the format really is, what lives inside it, and what to do when you need the contents as data rather than as mail.

What is an EML file?

An EML file stores one email message, complete, in a plain text format that follows the internet mail standards. The extension is short for electronic mail. Open one in Notepad or TextEdit and you will see readable text at the top: the From address, the To address, the Subject, the Date, a Message-ID, and a stack of Received lines recording every mail server the message passed through. Below the headers sits the body, and below that, if the sender attached anything, the attachment itself encoded as a long block of letters and numbers.

That is the whole format. There is no database, no index, no proprietary container. An EML file is the message as the mail servers saw it, written to a file. This is why it has survived for decades and why it is the format of choice for archiving, e-discovery, and moving mail between systems that otherwise share nothing.

What does an EML file contain?

Three layers, in order:

The MIME boundaries are the key to the whole thing. A multipart message declares a random boundary string in its Content-Type header, then repeats that string to separate each part. A parser walks those boundaries to figure out where the HTML body ends and the attached invoice begins. It is a simple scheme, and it is why a well-formed EML file is unambiguous to read by machine.

One consequence worth knowing: because attachments are encoded inline, an EML file containing a 4 MB PDF will itself be roughly 5.5 MB. Base64 inflates binary data by about a third. A folder of EML files is not small.

What programs open an EML file?

Most desktop mail clients read EML natively. Mozilla Thunderbird and Apple Mail both open them by double-click. Microsoft Outlook opens EML files and can import them, even though its own single-message format is different. On Windows, whether a double-click does anything depends on what is installed: with Outlook present the file usually opens in Outlook, and without a mail client Windows will ask you to choose an app.

Gmail is the common gap. Gmail's web interface has no option to open or import an individual EML file. You can attach one to a message and preview it, but there is no import button, which surprises people who assume a web mail client would handle the web's own mail format.

And the fallback that always works: any text editor. Notepad, TextEdit, VS Code, or less on a terminal will show you the raw message. You will not get a rendered HTML email, but you will see every header, which is exactly what you want when you are tracing where a message came from or debugging a delivery problem.

Why won't my EML file open?

Three causes cover nearly every case. First, no mail client is installed or associated with the extension, so the operating system does not know what to do; right-click, choose Open with, and pick a mail app or a text editor. Second, the file was renamed and is not actually MIME inside; open it in a text editor and check whether the first lines look like headers. Third, the file is truncated, usually from a failed export or a partial download, and clients tend to fail silently rather than tell you the message is incomplete.

EML vs MSG vs MBOX vs PST

Four formats get confused constantly, and the difference is really just how many messages each holds and who invented it.

If your export gave you a mix of the first two, the deeper breakdown in .eml vs .msg files explained covers which one to keep and why. The practical rule: EML travels anywhere, MSG keeps Outlook's private metadata, MBOX is a stack of EML messages in one file, and PST is a mailbox you need Outlook to crack open.

Can I open an EML file in Excel?

Not directly. Excel expects rows and columns, and an EML file is a MIME document with headers and encoded parts, so Excel has nothing to map to cells. Rename an EML to .csv and Excel will dump the raw headers into column A, which is worse than useless. The answer is to convert the message first, so each field you care about becomes a column. The full walkthrough lives in can you open an EML file in Excel.

How do I convert EML files to CSV or Excel?

Decide what a row means before you touch a tool. Usually one row is one email, and the columns are the values you want out of it: sender, date, subject, and then whatever business data sits in the body, such as an invoice number or an order total. Once you know your columns, a converter reads each EML file, extracts those fields, and writes the rows.

For a handful of messages, copying by hand is fine. For a folder, use a parser. The EML to CSV converter takes your files and returns one CSV with a row per message, and the EML to Excel converter does the same with a formatted workbook. If you need the same job done repeatedly on a live mailbox rather than on exported files, the broader email to Excel workflow connects the inbox directly. Step by step instructions are in how to convert EML files to CSV in bulk.

What about the attachments inside?

Extracting the message body is only half the job when the data you need is in the attached file. An EML archive from an accounts payable mailbox is really a pile of PDF invoices wearing an email costume, and pulling the totals means reading the attachment, not the message. The same is true of records held by real estate and legal teams, where the attachments are executed contracts and extracting the key dates and clauses from a commercial lease is a separate task from reading the email that delivered it. Know which layer your data lives in before you pick a tool, because a parser aimed at the body will happily return nothing while the numbers sit untouched in the PDF.

Are EML files safe to open?

The file itself is inert text. The risk is the same risk as any email: an attachment inside it may be malicious, and an HTML body may try to load remote content that confirms your address is live. Opening an unknown EML in a text editor is completely safe and shows you the headers and the attachment names without executing anything. Opening it in a mail client is as safe as your client's settings, so keep remote image loading off if you are examining something suspicious.

The short version

An EML file is one email message saved as MIME plain text: headers, body, and base64 attachments in a single open-standard file that any mail client or text editor can read. It differs from MSG (Outlook's binary single message), MBOX (many messages in one text file), and PST (a whole Outlook mailbox). Excel cannot read one directly, so convert it: point the EML to CSV converter at your folder and get one row per message, with the fields you actually need as columns.