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".

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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.