Is there web app that can open
.eml attachments properly?
(Updated) I did a search and found a service by a company named Encryptomatic. The web page lets you specify an .eml file (or other file formats such as .msg) from your computer. It will then render the contents of the file.
A note from a legal/privacy perspective: When you specify a file, you are essentially giving the service a copy of your file. I assume they are reading the copy and then deleting it, but I have no knowledge or connection with the company or the service.