Could you please elaborate your query ?
Based on the verbatim, I assume that you see the email in Dynamics 365.
Is the email received in Dynamics 365 or being sent from Dynamics 365 ?
How are you adding the Attachments to the email ?
What Security Roles are assigned to the current user who is trying to add attachments ?
Do you get any error while adding Attachments or you see no option to add an attachment ?