Could you please provide more details here? What is the sender address of the email? Have you connected this email address as a personal inbox in HubSpot or as a conversations inbox? Are the recipients all HubSpot users? Are the recipients HubSpot users who are also HubSpot contacts? If so, do the emails show on their contact records?
The more detail, the better.
Best regards
Karsten Köhler HubSpot Freelancer | RevOps & CRM Consultant | Community Hall of Famer