In this case prevention is definitely better than cure.
By default when you use the ZAP spider and active scanner then ZAP will access all of the URLs, forms, and functionality it can find. If one of those results in your application sending emails then someone is going to get a LOT of emails. (Consider other scenarios like sending orders, HR actions, helpdesk tickets, etc.)
If that has already happened then there is basically nothing you can do in ZAP to prevent those emails from being sent. You can stop the ZAP spider or scanner if it is still running, but ZAP will already have submitted the form many times and so the resulting emails will have been sent to your email server.
You may be able to stop the emails at the mail server (or maybe within the application, if it queues them) but that has nothing to do with ZAP.
The best option is to make sure that ZAP does not submit the relevant form(s) in the first place, or that you execute the tests in a non-production environment.
You can configure both the spider and active scanner to not submit any forms, but that will significantly reduce the effectiveness of these tools.
The best option is to explicitly exclude those pages from the spider and active scanner or from ZAP as a whole via 'exclusions' - these can be accessed via the right click 'Exclude from' menu or the Session Properties dialog.