At the moment when the incoming email channel is configured emails without a relation to an existing ticket will create a new ticket. Follow-up emails to a notification will be registered as a response on an existing ticket.
It would be nice if only follow-up email would be registered/allowed. We would like to ‘force’ our users to create a new ticket in Zammad first, so that they fill all the custom fields that we created. After they have done that it’s fine to add additional information to the ticket via email,. So just the initial ticket creation should be done manually.
I don’t see a way to configure this at the moment, you can either accept incoming email or don’t process incoming email at all.