Only active campaigns can be stopped. There is a two minute delay when sending email requests, so you can stop the emails within this timeframe if you change your mind.
To stop scheduled emails, first head over to your Contacts page and click the REQUESTS tab. If the status is Campaign Active next to the name, you can stop the scheduled emails.
Select the contact with scheduled requests and click Stop campaign from the blue menu bar.
When the popover opens, confirm the action.
Requests that have not yet been sent will be cancelled. Requests that have already been sent cannot be cancelled.
Once you stop the campaign, the status will change to Campaign Stopped. Emails that were successfully stopped before they went out will show as "Stopped". If emails were already sent, they will not be stopped and it cannot be unsent.