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v3 api returns Email address is invalid for no apparent reason

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The API call to the endpoint returns "Email address is invalid" for most calls. Here are five example email addresses all rejected as "invalid" (both by my production application and also using the "test" feature of the API docs):

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Thank you for reaching out to Constant Contact API Developer Support, my name is Caleb. My team is here to assist outside software developers with questions about building into Constant Contact's API.


The error message 'Invalid email address' is typically caused by our compliance system detecting multiple sign ups to several Constant Contact accounts from the email address that caused the error. I can confirm that all 5 of the listed examples have been detected as having signed up to multiple accounts in a short time causing the system to block sign ups from these addresses.


If you have further questions about these error messages please feel free to reach out to our Account Review department and they would be happy to answer any concerns you may have.


Contact an Account Review Specialist:



Caleb A.
API Support Specialist

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