Hustle does not accept emails with "-" in the domain

Trying to make a test-Subscription, i had to experience Hustle not accepting my email (test@mehr-freu.de) - but when i change to an address without colon, it works.

Bad thing: there ist not shown any error message, but a red exclamation mark.
Next bad thing: in Germany gathering email-adresses without Double-Opt-In is quite a risk. Is there a way to activate it in Hustle? (without EmailMarketingProvider added)
Or do you plan to add mautic.org to the list of your supported providers soon?

Can i change this myself or is there a patch?

System:
using on current WP4.7 with Hustle configured for email list only
incident occurs in all types of view (Popup, Widget, Slidein)