You probably have found there is no whitelist for a specific bounced email in Xenforo (as far as I have found).
Is your handler automatic? Automatic is either on or off for all users. To make it a manual bounce handler go to Setup > Options > Email options > Bounced email address: and clear that field. Then the handler will use the default email for bounced email review. You also need to disable Enable automated bounce handling:
To make it so that no bounced emails are sent just use a dummy email in the Bounced email address field, however that can cause problems depending on how many are actually bounced.