While there is not a mechanism in place that would automatically update both your database and Constant Contact, however there are some methods that you could use to keep them in sync.
1. You could make your sign up form perform both operations, that way whenever a user signs up they are automatically placed into your database as well as your Constant Contact account. For more information on how to add a single contact using our API, please take a look at Creating a Contact.
2. Your other option would be to leverage our Searching for Contacts by Last Updated Date (Synchronizing Contacts). This will allow you to query only the updated contacts since a specified date. You can query by either a particular list type (active, do-not-mail, removed) or a particular list in your account. If you plan to keep your database in sync with our database, we recommend running this API periodically to ensure that your database is up-to-date and the number of contacts you need to deal with is not very large.
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