EML vs MSG: Which to Choose When You Save an Email

An EML file and an MSG file each hold one email. What differs is how they are built: EML is the message exactly as it travels between mail servers, while MSG is an Outlook item written out to a file. That difference decides which apps can open them and which format each app saves in.

If the file you have is a .msg, the MSG viewer on this site opens it.

What is inside (open them in a text editor)

An EML file is plain text in the format of internet mail (RFC 5322). Open one in Notepad and you see the sender and subject fields. This is the start of the sample EML this site uses:

From: Sample Sender <sender@example.com>
To: Sample Recipient <recipient@example.com>
Subject: =?UTF-8?B?5Zub5Y2K5pyf44Os44Od44O844OI44Gu6YCB5LuY?=
Date: Wed, 25 Feb 2026 10:14:00 +0900
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="----=_Part_0_1706000000000"

A subject with any non-ASCII characters is written in the =?UTF-8?B?…?= form and cannot be read as it stands. The body and any attachments follow as text, with attachments turned into long runs of letters, digits and symbols.

An MSG file, according to Microsoft's specification ([MS-OXMSG]), is a "compound file": a single file holding a hierarchy of storages and streams, a little like folders and files. The same format stores Outlook appointments, contacts and tasks as well as emails. A text editor shows nothing readable, and the file always starts with these eight bytes:

D0 CF 11 E0 A1 B1 1A E1

That is the same container signature as old Word and Excel files (.doc, .xls). The subject and body sit inside the container as properties of the Outlook item.

How each app saves a message

Which file you get depends on the app you save from. This is what each company's documentation says:

Sources: Microsoft's "Save an Outlook message as a .eml file, a PDF file, or as a draft", Gmail Help, the Mail User Guide for Mac, and Microsoft's "Outlook for Mac features". For classic Outlook's save types, Microsoft's help only says to "accept the default type, or choose another file type in the list", and we found no Microsoft document listing the types as they appear on screen. The list of save formats Microsoft publishes for developers (Outlook's OlSaveAsType) has no EML, although that list is not the same thing as the on-screen list.

Which apps open them

Sources: Microsoft's "Feature comparison between new Outlook and classic Outlook", "Open .eml, .msg, and .oft files in new Outlook and Outlook on the web" and "Outlook for Mac features", and the release notes for Office for Mac. "Not documented" means the help says nothing either way.

This site's viewers read the file inside your browser without sending it anywhere. They show the subject, sender, recipients, date and body, and save the attachments one by one or together as a ZIP. They do not convert between EML and MSG.

Saving as MSG? Pick Unicode

Classic Outlook's Save as type list has two MSG types, one with "Unicode" in its name and one without (in Microsoft's developer list, "Outlook Unicode message format" and "Outlook message format").

Microsoft's help describes Unicode as an encoding "that enables most of the written languages in the world to be represented by using a single character set", and says that if you share messages with people who use classic Outlook on computers that run in other languages, you can take advantage of it. A non-Unicode MSG stores all of its string properties, such as the subject and the plain-text body, in a code page for one particular language (Microsoft's specification [MS-OXMSG]). Which code page is left to information outside the string itself ([MS-OXCDATA]), so a reader that assumes a different one can show garbled text.

To save in Unicode every time, go to File > Options > Mail and, under Save messages, select Use Unicode Format (from the same Microsoft article).

Which to choose

• To hand to someone, or to read later in another app — EML if you can choose it. New Outlook and Outlook on the web open it without a Microsoft 365 subscription (MSG needs one), and Outlook for Mac opens it from 16.58 (MSG only from 16.108).
• You only have classic Outlook for Windows — EML is not offered, so save as MSG (Unicode). If the other person has no Outlook, point them to this site's MSG viewer.
• You want Outlook appointments or contacts as files too — MSG stores them in the same format. EML is a format for emails, so appointments and contacts do not fit in it. There are also the standard .ics (appointments) and .vcf (contacts) formats, which are in Microsoft's developer list of save formats too.