Step 1: From Admin Dashboard, go to Setup -> Settingd and click on "Third Party Integration".
Step 2: Then click on "Constant Contact Integration".
Step 3: Followed by that, click on "Connect to Constant Contact".
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.