Mail encoding issue

[gxHL]

Hi I have a weird issue with my VestaCP installation. The mail orders I receive from my opencart online store are shown very weird. Please take a look at this screenshot https://i.imgur.com/4VRkK1I.png

Downloading the .eml file and opening it up with Thunderbird is working correctly. Here is the view source of the email https://pastebin.com/1ehDaAbS

Any ideas on how to fix this issue?

Ubuntu 16.04