Viewing and Understanding Email Internet Transport Headers in .EML Files

A screen shot of Pst Viewer Pro displaying email internet header info.

An EML (Electronic Mail) file is an open file format used to store individual email messages. It is a standard file format often associated with email clients like Thunderbird that follow the MIME (Multipurpose Internet Mail Extensions) standard. EML files contain the complete content of an email message, including the text, attachments, and metadata.

An email internet transport header, also known as an email header or message header, is a block of metadata information that provides details about the origin, route, and content of an email message. This information is not typically visible in the body of the email when you read it but can be viewed by accessing the email’s header section.

Email internet headers are usually not visible to users. A useful tool for managing EML files and viewing the internet header is a Pst Viewer Pro (formerly known as EML Viewer Pro) by Encryptomatic LLC, a U.S. based software developer.

Here are some key components typically found in an email internet header:

  1. Return-Path:
  • The email address to which bounce notifications and delivery errors are sent.
  1. Received:
  • This section contains information about the servers through which the email passed on its way to the recipient. It includes details like the server’s IP address, timestamp, and authentication information.
  1. From:
  • The email address of the sender.
  1. To:
  • The email address of the recipient.
  1. Subject:
  • The subject line of the email.
  1. Date:
  • The timestamp indicating when the email was sent.
  1. Message-ID:
  • A unique identifier assigned to the email for tracking and reference purposes.
  1. MIME-Version:
  • The version of the Multipurpose Internet Mail Extensions (MIME) standard used in the email. MIME is a standard that extends the format of email messages to support text in character sets other than ASCII, as well as attachments of audio, video, images, and application programs.
  1. Content-Type:
  • Specifies the type of content contained in the email, such as text, HTML, or attachments.
  1. X-Headers:
    • Additional custom headers that may be added by email servers or applications for specific purposes.

The email header is crucial for various reasons, including:

  • Routing Information: It shows the servers and paths the email took to reach its destination.
  • Authentication: Some headers provide information on email authentication methods used, helping to verify the legitimacy of the sender.
  • Spam Filtering: Email headers can contain information used by spam filters to assess the likelihood that an email is spam.
  • Troubleshooting: When dealing with email delivery issues, the header can be analyzed to identify potential problems in the routing process.

To view the email header in most email clients, you can look for an option like “View Source,” “Show Original,” or “View Message Source.” Analyzing email headers can be useful in understanding the journey of an email and in troubleshooting email-related problems.

Get a free 15 day trial of Pst Viewer Pro for Windows 11/10.

Comparing Four .Eml File Viewers

Encryptomatic LLC logo

.EML files are email messages that are text encoded files, formatted according to RFC-822, an open standard.  There are several Windows software applications that will open .eml files.  To  save time and money, the capabilities of the .eml viewer you select should closely match your needs.  For example, if you only have a few .eml messages to open, you could use a free online solution.  If your need is for bulk email archiving, or converting many eml files into pdf files, you’ll want a viewer that is able to search and manage thousands of .eml files at once.

This article looks at four different products for opening .eml files.  We’ve arranged these solutions based on their capabilities, from least to greatest. We hope one of them will match your specific needs. All of them offer free trial downloads, so you can make sure it’s the best .eml viewer for your needs.

MessageViewer Online

If you only have a few .eml files that you want to read, try MessageViewer Online, a free online .eml viewer. To use MessageViewer Online, you upload your .eml file. The email is converted into a web page and is then displayed in your web browser.  Email file attachments can be downloaded by clicking on a link.

An .eml file was uploaded to MessageViewer Online and is displayed in a web browser.
.EML file displayed with MessageViewer Online

In addition to .eml files, MessageViewer online can also open .msg and winmail.dat files. The emails are deleted within moments after your session ends. This is a free service offered by the developer, Encryptomatic LLC, to demonstrate a commercial email parsing software component. No information is retained or collected from the email files.

An alternative to using MessageViewer Online would be to install a free email client that can open .eml files, such as Mozilla Thunderbird.

MessageViewer Lite

MessageViewer Lite is an affordable email viewer  ($24.99) for Windows. It opens .eml, .msg and winmail.dat files.  MessageViewer Lite was the inspiration for MessageViewer Online, and uses the same email rendering engine.

MessageViewer Lite is a favorite of system administrators who want to deploy a quality email viewing tool for their clients. It can be set as the Windows default file handler, so opening .eml or .msg files is as easy as clicking on them.  Multiple viewing windows may be open simultaneously. Text can be copied from the email, and the .eml file can be printed.  File attachments can be saved to a folder with drag and drop ease.  If you need a simple .eml viewer that has no learning curve and that has been tested in enterprise environments (.msi installer file is available), then MessageViewer Lite should be on your short list.

Affordable .eml viewer for Windows, main screen showing a email message.
MessageViewer Lite, affordable .eml viewer for Windows


MessageViewer Lite .eml viewer, file menu drop down.
MessageViewer Lite File menu


EML Viewer Lite

EML Viewer Lite ($29.99, also known as Pst Viewer Lite) has many more capabilities than MessageViewer Lite. It can browse and search a directory of thousands of .eml files. It also opens Outlook .pst, .msg and winmail.dat files.

Eml Viewer Pro displaying a html .eml file.
EML Viewer Lite main screen


Eml Viewer Lite main screen.
EML Viewer Lite Mail Menu.
Eml Viewer Lite menu items.
EML Viewer Lite toolbar puts important functions front and center
Saving .eml files as .MHTML files.
Convert an email to PDF, HTML, MHT and other formats

Emails can be individually printed, or converted to different formats, including PDF, HTML, MHT, Text, PNG, GIF, BMP or TIFF.

EmlViewer Lite tools are selectable from the toolbar.
EML Viewer Lite toolbar

The EML Viewer Lite makes it easy to reply, forward or reply-all to .eml files using your Windows default email client.  You can also individually add .eml files to an existing pdf file, creating a PDF suitcase of emails.

EML Viewer Lite gives you a lot of high-end email content management functionality at a very low price. An MSI installer is available for enterprise deployment, and a 15 day free trial is available from the product website.

EML Viewer Pro

EML Viewer Pro ($79.99)  is the most capable eml file viewer on the market. It has all of the same features as the Lite version, and a lot more.  EML Viewer Pro will open .eml files, as well as .pst, .ost, .msg, winmail.dat, and .mhtml files.   Email messages can be converted individually or in bulk to many formats, including .pdf, mbox, eml, csv (Excel), text, and image formats such as jpg, gif, tiff, bmp and png.

The main difference between Pro and Lite is the export function. While Lite can export emails individually, Pro can convert or print them in batches of thousands of emails.

EmlViewer Pro email list organizes .eml email files.
EML Viewer Pro application window

EML Viewer Pro lets you setup custom export profiles that can accomplish multiple tasks in one operation, such as applying a specific naming scheme to the files it creates. It can export multiple emails into a single PDF file. There are several options for managing .eml file attachments while converting to PDF. For example, you tell EML Viewer Pro to try and convert the attachments into the PDF image, embed the attachments as files, extract the file attachments to a folder, or ignore them altogether.

EML Viewer Pro supports bulk printing of emails, and bulk conversion to PDF.  A MSI file is available for enterprise deployment.

Pick your eml viewer

When choosing a viewer for opening .eml files, its important to get the one with the capabilities you require.  Whether your needs are simple or very complex, one of these four eml viewers should help you accomplish your goal. Download a trial of the eml viewer that is closest to your needs and try it out free for fifteen days.