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Using the Letterhead API

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The Letterhead API allows you to programmatically access newsletters, audiences, metrics, and content. Two API versions are available — v2 for organization-level operations and v3 for company-level operations — both using Bearer token authentication.

API versions

Section titled “API versions”

v2 (Organization-scoped)

  • Operates at the organization or brand level
  • Use for operations scoped to a single organization and its channels

v3 (Company-scoped)

  • Operates at the company level, across every organization and channel in your account
  • Use for company-wide operations, such as managing your whole audience

Authentication

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All API requests require a Bearer token in the Authorization header:

Authorization: Bearer <your-api-key>

Generate a key of the matching scope (v2 or v3) in your account settings — see Generate & manage API keys.

What you can build

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  • Add, update, or remove subscribers, and set subscription status
  • Push articles into your Curations library
  • Pull performance metrics and reporting data
  • Retrieve newsletter audience overlap data — shared subscriber counts for every pair of newsletters, and combined unique reach for any two to five

API reference

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The complete endpoint reference — request/response formats, parameters, and error codes — is in the Letterhead API documentation. Use it as the source of truth for endpoint URLs.

Next steps

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Still can’t find what you need? Contact support.