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Hello Joyce,

This is happening because of trigger named "Notify requester of comment update" so based on your use-case you can change this trigger action.

for Newly created ticket refer "Notify requester of received request" trigger 

Hey Joyce,

As Sushant mentioned, the Notify requester of received request trigger located under Admin>Business Rules>Triggers is what's sending out this email notification every time a new ticket is created. Once you disable this Trigger, the email notifications should stop.

More on default triggers here: About the Support default triggers

Hope this helps!