Being able to send from an address doesn't necessarily mean that it's technically possible to receive emails under that same address. HubSpot would allow you to send from a non-existent address, as long as that email domain is connected.
This is something you would have to address outside of HubSpot, in the settings of your email service provider or in your email guidelines. Does that sending address accept emails from outside of your organization, for example? If not, that would explain why your reply goes through, external replies don't.
The details will be documented in the mail delivery failure description. This will typically state the exact reason. Without those details, it's not possible to say what exactly is causing this.
Share this error with your IT and they should be able to make adjustments accordingly.
Best regards!
Karsten Köhler HubSpot Freelancer | RevOps & CRM Consultant | Community Hall of Famer