Thank you for reporting this critical bug; we understand the problem is that the Email Marketer is sending multiple emails for a single order if it contains more than one unit of the same product.
For more information, please see:
https://docs.whmcs.com/8-13/system/email/email-campaigns/#Internal_Queue_vs._External_Send_Requests https://mycabinquiz.com/
We agree this is not the intended behavior and will ensure the tool's logic is corrected to send only one email per product per order to avoid spamming。