You can definitely pause a Email Marketing Autoresponder, after you've started it. When you first create a new campaign, it actually starts as paused for you, by default. This way, it doesn’t start sending until you’re ready :)
You can see the status of a current campaign in the top right corner of your Autoresponder area, to the right of the individual campaign title. To get things started, you click on Run Campaign, at the bottom of the thumbnail preview.
If you want to pause a campaign that’s running, you can click on Pause Campaign at any time.