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.

Transitioning email from the client to the cloud.

“While the cloud is both the present and the future of email, it’s important to the enterprise to let employees retain the trove of data that resides in their local email repository.

It doesn’t happen very often in a client server environment, but every now and then a large corporation will find itself in the middle of email client platform change. The reason companies are loath to change how users interface with email is because, well, its a big deal to employees. And now as a platform shift is underway with email migrating to the cloud, many companies and their employees are struggling to answer the question:  “How are we going to manage our legacy email.”

People who have meticulously organized years worth of emails into folders, and sub-folders and sub-sub-folders resist the idea of migrating to a different email client, or will at least insist on being allowed to retain local access to this content.  While enterprise archiving tools are supposed to ease the transition, users often express that such systems fall short for useability and convenient access.

And companies may have CRM systems where .eml or .msg formatted emails have been attached to client records. If Outlook is migrated to the cloud, with no local application set as the default for .msg files, accessing email content can become a frustrating ordeal.

The problem with leaving a legacy email client installed is that people will want to continue using it, even though the administrators want usage pushed to the cloud.

One way to satisfy the needs of both the users (who need local access) and email administrators (who want users to move on) is to install an email viewing application in place of the client. This helps facilitate the transition to the cloud or a new client, ensuring some backwards compatibility and retaining the knowledge that resides in the legacy email.

A very popular email viewer for enterprise use is Pst Viewer Pro. Although named for Outlook .pst files, PST Viewer Pro can easily manage piles of Windows Mail or Thunderbird .eml files, as well as Outlook .msg files. PstViewer Pro does not require any help from Outlook to access email files, and can render even the most complicated emails accurately.  Employees can use its search function to find important emails, and can reply, print or export emails to PDF and other formats.

For employees that truly just need “click to open” access to EML and MSG email files, there is a lite version of PstViewer, called Message Viewer Lite. This easy to use no frills software is super simple. Users just click on an email file, and it opens.  They can print it, copy text, and access file attachments.  Both PstViewer and MessageViewer Lite are available as .msi files for easy mass deployment to dozens or thousands of employee desktops.

While the cloud is both the present and the future of email, its important to let your employees retain the trove of data that resides in their local email stash. Using a transitional technology such as an email viewer can make that transition go much more smoothly for employees and email administrators alike.