@Stephan.J, you may find this thread interesting.
I am not sure if official mailgun support is coming or not, but it looks like a much simpler solution that requires no RPi running a server. Perhaps @chuck.schwer will chime in to let us know if this is something on the list of upcoming feature enhancements or not? 
Hubitat currently supports Push Notifications via the Hubitat Mobile App and via Pushover. Hubitat also supports SMS text messaging via Twilio. Just making sure you’re aware of some other officially supported options.
