You can set a BCC email address in the company settings, a copy of invoice emails and reminder emails will get sent to this email address then.
Which Billing module version do you use? I checked the code of the 1.4.1 release and this version sends the reminder as bcc email to the address that is defined as bcc in the company details.
Hi, The issue is between the chair and the keyboard. I have a rule to push the email in a dedicated folder Sorry for the inconvenience Best regards