In the case that you want to globally turn off all notifications and ticket deliveries for all your events head over to Settings -> Order Settings and enable the feature "Never send notification email to customers when tickets are purchased or created with their email address."
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Please note this will prevent all ticket deliveries and any kind of communication via email.
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If you wish to control a specific event please go into the selected event - > "Event settings" and enable the feature "I'll manually trigger it, never automatically send tickets."

Evey will then wait for your approval before sending any tickets.
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