Hello @user8257676 ,
You can look up on the internet to see if there's any integrations that have been developed for whatever you use to host your store your contacts and our system, or see if there's a known 3rd party option under the Integrations tab in your account.
Otherwise, systems that store contacts usually have a way to export them as a CSV file type. If you can do that, you can manually import the file into your Constant Contact account.
Formatting contact files for clean imports
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