It is possible to stop the sending of a scheduled email, even after it has starting sending, by changing the status of the email from "Sending" to "Draft."
As you can see in the gif below, you simply:
- Click on the Email
- Click to Edit
- Change the Status
- Hit Save
You will then see two emails:
- One with a status "Send" - this is one that will be linked to all the people who will receive the email before you were able to change the status
- One with status of "Draft" - this includes all the people who will not receive the email because you changed the status before it was sent to them
