Amazon recently implemented a new option that allows the buyers to opt-out of unsolicited messages sent from third-party merchants. Buyers who turn on the "Do not send me any marketing email for now" in their Amazon account will no longer receive marketing messages from your Seller Account.

Our understanding right now is that once it is turned on by the buyer, all messages going to those buyers will be blocked. Until Amazon releases the opt-out status in the order or API, the only way to identify buyers who have opted out is through Amazon’s bounceback email.

To avoid sending further emails to those buyers who have opted out, users can simply setup BQool email for the Buyer Opt-out emails to avoid sending emails to those Buyers who’ve opted-out in the future. Once the BQool email has been added to your opt-out section in Amazon Notification Preferences, we will no longer send emails to that buyer from any BQool user account.

Please refer to the support article here for further setup instruction. 

How to Configure Your Buyer Opt-Out Email System

If you would like to know more about the new Buyer opt-out situation, please go to Buyer Opt-Out Email and What You Should Do.