Problem with using Mailgun and EU region

[SumeraMartin]

Describe the bug
I'm using mailgun and eu region which forces me to change host for the API and it seems like that this is not possible to setup otherwise I'm getting Forbidden error.

From documentation:

host - the mailgun host (default: 'api.mailgun.net'). Note that if you are using the EU region the host should be set to 'api.eu.mailgun.net'

https://github.com/paralect/mailgun-js

Expected behavior
Would be nice to be able to define it as env property and pass ti to mailgun