If you're working with our Conversations tool, you can get notified when an email reply arrives in your Conversations inbox.
If you are, however, sending emails from CRM records with your connected personal email, you unfortunately cannot get notified about replies, but you do get notifications about email opens and the following actions in your Activity feed:
I understand your use case here - other users have already posted about this feature in our Ideas forum, you can see the feature request here. We use the Ideas forum to collect ideas on how we can improve the product for our customers. Product pays particular attention to the top voted ideas & takes them into consideration along with other feedback channels - it would therefore be great if you can give the idea an upvote. Thank you!
P.S.: You can also reply or post new questions in the Community in German if you wish, there are also German-speaking HubSpot experts here in the DACH Community who would be glad to help you with questions 🙂