When you get an e-mail with *.eml attachments save the eml attachment to your Computers temp directory; best if you create a separate directory in /tmp like /tmp/juno

To unpack the eml file you need to install the mpack package.

sudo apt-get update && sudo apt-get install mpack

Go to the location you saved the eml file.

cd /tmp/juno
munpack file.eml

Files in the eml get unpacked and are locate in /tmp/juno

How to open eml files?