Retrieve newsletter audience overlap data via API

Overview

The Letterhead API provides endpoints to analyze how much your newsletters’ audiences overlap. This helps you understand subscriber relationships across your publications and measure your combined reach. This data is available over the API only.

What you can retrieve

The API provides two types of overlap data:

Pairwise overlap for all newsletters:

How many active subscribers each pair of newsletters shares
Total subscriber count for each newsletter
Complete view across your entire portfolio

Detailed breakdown for specific newsletters:

Combined unique reach across two to five selected newsletters
Number of subscribers shared across all selected newsletters
Number of subscribers exclusive to each newsletter

Use cases

This data helps you:

Identify which newsletters share the most subscribers
Calculate your true unique reach across multiple publications
Make informed decisions about cross-promotion opportunities
Understand audience segmentation across your portfolio

Next steps

Refer to the API documentation for endpoint details, authentication requirements, and response formats.

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