Is It Possible to Stop an Email Campaign From Sending?

You can’t unsend a campaign that’s already been sent. However, you can stop a campaign from sending up until the designated send time. To check for mistakes, you can send test emails to yourself and up to 20 recipients at a time as many times as you want.

You can stop scheduled and automated campaigns from sending by deleting or disabling the campaign. Navigate to Campaigns > Scheduled or Automation and click on Delete, Stop or Disable. 

1) Scheduled Campaign

2) Automated Campaign