How do I stop emails to all users in Zendesk when I create/test in sandbox?

Hi Arielle B, 

You might want to check on the ticket events first to see what trigger is causing it. After that, you'll just need to deactivate that trigger. 

Here's how. : https://support.zendesk.com/hc/en-us/articles/4408882237722-Managing-triggers#topic_jvv_kqy_tb

To deactivate a trigger

1. In Admin Center, click  Objects and rules in the sidebar, then select Business rules > Triggers.
2. On the Triggers page, locate the trigger you want to deactivate.
3. Hover your mouse over the trigger to display the options menu icon () and select Deactivate. The trigger’s status is changed to Inactive.