generated: '2026-06-20'
method: searched
source: https://mailchimp.com/developer/release-notes/
docs: https://mailchimp.com/developer/release-notes/
description: >-
  Structured capture of the recent window of Mailchimp's dated developer release
  notes (covering both the Marketing and Transactional APIs). The live release
  notes are the source of truth; this records the most recent entries. Mailchimp
  does not use semantic version tags — changes are announced by date.
versioning:
  scheme: 'date-announced (major APIs are URI-path versioned: Marketing v3.0, Transactional v1.0)'
  detail: lifecycle/mailchimp-lifecycle.yml
entries:
  - date: '2025-08-19'
    title: Mailchimp Transactional status added to server status page
    additions:
      - Live status tracking for Transactional API servers on the Mailchimp status page.
  - date: '2025-08-07'
    title: New Audiences endpoints (BETA)
    additions:
      - Beta endpoints to create contacts using SMS numbers without an email address.
  - date: '2024-12-06'
    title: Overwriting campaign_id and outreach_id
    changes:
      - System auto-overwrites campaign_id and outreach_id to align with the new attribution model.
  - date: '2024-06-17'
    title: Webhook retry interval increased
    changes:
      - Webhooks now retry up to 20 times at 15-25 minute intervals before being disabled.
  - date: '2024-02-12'
    title: Updated Mailchimp Transactional client libraries
    changes:
      - PHP and Node.js libraries updated for PHP 8.2 compatibility and an Axios security fix.
  - date: '2023-12-19'
    title: New sending domain authentication requirements
    breaking:
      - DKIM and DMARC policy requirements enforced starting 2024-03-15.
  - date: '2023-06-17'
    title: Response code updated for invalid template name
    breaking:
      - Invalid template requests now return HTTP 404 instead of HTTP 500.
  - date: '2023-06-05'
    title: Retiring legacy TLS protocol versions
    breaking:
      - TLS 1.0/1.1 support ended 2023-07-18; TLS 1.2+ now required.