That’s no feature request and technically correct behaviour by Zammad.
The reason for that is that a bounce never contains reference information that would help Zammad to recognize e.g. follow ups.
Also, technically, there’s no loop happening here. Those mails you’re talking about are triggered based on the notification settings of the affected agent and might be independent.
You can’t overcome this issue, because Zammad can’t determine why the bounce occured.
That’s nothing we can solve, sorry.
Thanks for your input MrGeneration, I understand that this is not illegal behavior, but it does create a flood storm.
I have seen other ticketing systems implement flood protection with exponential backoff, e.g. if a customer submits $NUMBER of tickets in $TIME then flood protection will reject further tickets for $WAIT_PERIOD.
More advanced solutions will increase $WAIT_PERIOD according to an exponential scale (or Fibonacci sequence) if flood protection is triggered within $WAIT_PEROIOD+$TIME.