Step 1: From Admin Dashboard, go to Setup -> Setting
Step 2: Then click on The Third Party Integration.
Step 3: Followed by that, click on Constant contact integration
Step 4: Login to your Constant Contact Account.
Step 5: After login, click "Allow".
Step 6: Once you select the list and save it, new users will be automatically added to the Constant Contact list.
Step 7: For disconnecting from Constant Contact, just click “Disconnect” and new users would NOT be added to the Constant Contact automatically.