Thank you for reaching out to Constant Contact API Developer Support. My team is here to assist outside software developers with questions about building into Constant Contact's API.
You are correct, data can only be sent between Constant Contact and a 3rd party via our APIs at this time.
The only webhooks we currently offer are for Partner accounts (and those are only related to account billing within a partnership). We don't currently offer any webhooks for individual accounts' contacts, campaigns, etc.
Please have a look and let us know if you have any other questions!
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