What Are EML Files?

Files with the .eml extensionare email files that store the content, headers, and pictures included in an email. They can also contain any email attachments, so the file size can be large.

In general, .eml files are created by Microsoft Outlook or other similar email programs when someone receives or saves an email. If someone has sent you a .eml file and you don’t have Outlook on your system, you can still open it through other programs, though.

You can easily open .eml files with Microsoft Outlook Express, Windows Mail, or Mozilla Thunderbird. On a Mac, Apple Mail is always included as a default program and will open .eml files, or the Microsoft program suite includes a version of Outlook that can open .eml files. Eml viewer software programs can process these files if its not desirable to install a full fledged email client application.

Another option for advanced users is to open the .eml files you receive with Internet Explorer, Opera, or another web browser. The compatibility varies depending on the browser software and version you have, the content of the email and so on, but if you’re desperate for another option, this might work. If you can’t figure out how to do this, you can change the file extension from .eml to .mht and it may work. EML and MHT files are very similar, except that MHT files do not have the email header information. For some people, understanding how to change a file extension may be difficult, and it may be impossible if you are operating from a Windows account without Administrator privileges.

While the average .eml file should be accessible through an e-mail application or web browser, if this doesn’t work you could try to email the sender of the .eml file and ask them to forward the original email to you as text instead.
If you have many .EML files that you need to search or process, you can try a .EML file viewer.  PST Viewer Pro is one such viewer that is able to work with many different file types such as .EML, .MSG, .PST, .OST and even .MHT files.  Click here for more information on PST Viewer Pro https://www.encryptomatic.com/emlviewer/ and to download a free trial.
Review the specification for RFC 2822, Internet Messaging standard. or read “What Is .EML” for more information on .eml documents.

How to View a Windows Mail .EML File?

So you have a Windows Mail .eml file?  What is it, and how can you make sense of it?

 It is quite common to encounter .eml files as email attachments.  To understand them, let’s consider how a .eml file may come to exist.  If you are a Windows Live Mail user, you may find that the process to save a e-mail message as a .eml file is quite simple. Knowing how this is done makes it easy to share messages with someone without having to forward the message. Sometimes the context of the email message is best preserved when the message is shared in its entirety as a separate file. EML files can simply be included in an email message as a file attachments, while a forwarded message is more susceptible to manipulation.
To create a .eml file using Windows Live Mail, start by going to the program’s main menu.   Second, single click on any email displayed in the message list (don’t open it, just highlight it).  Third, click the the far left button in the tool ribbon, choose “Save as File,” and the select a location to save the file.  Your message will be saved as a .eml file.
Windows live mail screen shot.
Saving a Windows Mail message as .eml (1)
Saving an email in Windows Live Mail as a .eml file.
In Windows Mail, save the message as a .eml file
Another way to create a .eml file from Windows Live Mail is to just drag it out of the inbox and drop it on your desktop. That works, too.

What is a .EML file?

If you want to get technical about it, a  file with a .eml extension should conform to RFC-2822, the internet message format.  This standard establishes a common syntax for text messages so they can be sent between computer users as e-mail. Each .eml file contains a single email message (unless of course another .eml file is embedded inside of the .eml file, but each .eml file is really a separate instance of an email message).  
Most .EML files you will encounter are created by popular email clients such as Microsoft Outlook Express, Windows Live Mail, or Mozilla Thunderbird.  To create a .eml file using either of those two email clients, all you have to do is drag an email message from the inbox and drop it on your desktop.  Voila! Instant .eml file which will contain a header in plain ASCII text,  the main body of the message (text or html), and any file attachments associated with the email, such as spreadsheets, jpg pictures, videos, or text documents.
.EML files can range in size from 1 kilobyte to many megabytes, depending of course on what the sender has chosen to put into the file.
The truth is, not all .eml files conform exactly to RFC-2822. In the wild, you are likely to encounter many exceptions. Different software products that generate .eml files sometimes fail to implement the entire RFC standard. When this happens, emails may not be formatted correctly, or are unable to be opened.  PstViewer Pro is a .eml viewer software application that has identified dozens of these exceptions, and is therefore able to render many non-standard .eml files.
Often many email messages are grouped into larger files, such as a .PST file (Outlook) or a MBOX file (Thunderbird).  While Thunderbird and Windows Mail will allow you to save a single message as a .eml file, Microsoft Outlook does not allow this. Rather, Outlook saves individual emails as a .msg file, which is a Microsoft Office message format that is not RFC-2822 compatible.  As of Outlook 2010, Microsoft Outlook does not save email messages as .eml files.  MessageExport is a third party add-in for Microsoft Outlook that adds this ability to Outlook, allowing Outlook emails to be stored in EML format.