1. Log in to your Merchant Center and navigate to the "Settings" tab
2. Click "Customization" on the left-hand menu
3. Click "Edit Send Limit" next to "Automatic send limit is on"
4. Click "Automatically" and choose "Manually" from the drop-down menu that appears
5. Choose the maximum number of email campaigns you would like each unresponsive contact to receive from the drop-down menu that appears
6. Click "Update Limit" to save your changes