Stop automatic replies

My wife created an Apple Mail rule to send Out of Office replies but accidentally clicked the button to apply the rule to all existing messages in the inbox. The inbox is around 5000 messages so now for ever single message ever received, we are sending and out of office reply. While the rule has already been deleted, I’m guessing there is a queue and the automatic replies are still being sent.

Is there anywhere server side where I can stop it or is it too late?

If you are familiar with Postfix, you can delete the outgoing mail queue. Sorry, I cannot advise how to do so from the command line. :frowning:
I install WebMin on my MiaB servers (unsupported modification) and it is VERY easy to delete the mail queue with it. Perhaps, you can find the command line instructions with a Google search for ‘postfix delete outgoing mail queue’. Though by now it is probably too late.