Workaround to open Outlook and Outlook Express emails (*.eml) when you don't have Outlook installed

EML files are a file format developed by Microsoft for Outlook and Outlook Express.

An EML file is an archived email that preserves the original HTML formatting and headers. Most mail clients support EML files, but if you don't have an email client installed, or are using a mobile device, one of the workarounds to open the file is to change the extension to view it in a browser. EML files are very similar to MHTML, and changing the file extension to *.mht will quickly convert it into a format that can be opened in Internet Explorer.

While other web browsers can open MHT files, Microsoft Edge is the only one which will format them correctly. This method won't allow you to download any attachments.

Enable file extensions if you have them hidden
In Windows 10, search for File Explorer Options in the Start search box
In the opened window, click the View tab and uncheck "Hide extensions for known file types" in the Advanced settings
Right-click on the EML file and select "Rename"
Delete the .eml extension and replace it with .mht (Windows will warn you that this could cause problems with the file)
Confirm that you want to change the extension
Open the file in Microsoft Edge. This will usually be the default program for MHT files. You can right-click the file, select "Open with", and then choose Microsoft Edge from the list. Microsoft Edge will display the MHT file in virtually the same format as the EML file would appear in a mail client.