generated: '2026-08-12'
method: searched
source: https://products.zetaglobal.com/sailthru/Content/developers/api-basics/postbacks.html
docs: https://products.zetaglobal.com/sailthru/Content/developers/api-basics/postbacks.html
api: sailthru:sailthru-api
spec_type: none
asyncapi: false
note: >-
  Sailthru publishes no AsyncAPI document. Its event surface is "API
  postbacks": Sailthru POSTs to a customer-hosted URL when a specific
  lifecycle event occurs. There are four documented postback types. Delivery
  is authenticated with the same shared-secret scheme as the API — api_key
  plus a sig hash over all parameter values — so the receiver can verify
  origin. There is no event catalog beyond these four, no subscription API
  (URLs are configured in the application's API & Postbacks settings, and
  update postbacks must be enabled by a customer success representative), and
  no documented retry/backoff policy. A separate webhook step exists inside
  Lifecycle Optimizer for outbound calls from a journey, which is a workflow
  action rather than a subscribable event stream.
transport: HTTPS POST to a customer-hosted URL
authentication:
  mechanism: shared-secret signature
  parameters: [api_key, sig]
configuration:
  ui: API & Postbacks settings
  per_type_urls: true
  note: A different URL may optionally be supplied for each postback type.
receiver_contract:
  success_status: 200
  failure_statuses: [403, 500]
  note: >-
    Response codes are recorded in the account audit log, which is the
    documented way to confirm a postback is being processed.
retry_policy: null
events:
- name: verify
  action: verify
  description: Confirms a double opt-in verification succeeded.
  fields: [email, send_id, action, api_key, sig]
- name: optout
  action: optout
  description: Fires when a user opts out of, or back into, delivery.
  fields: [email, mode, optout, action, api_key, sig]
  optional_fields: [blast_id, reason, list, message_id]
  notes: 'mode is all or basic; optout is 1 or 0.'
- name: update
  action: update
  description: >-
    Fires when a user changes subscriptions or custom fields on a
    Sailthru-hosted page. Must be enabled by a customer success representative.
  fields: [sid, email, page, optout_email, lists, vars, action, api_key, sig]
- name: hardbounce
  action: hardbounce
  description: Notifies of a permanent delivery failure.
  fields: [email, send_id, blast_id, action, api_key, sig]
  notes: Carries send_id or blast_id depending on the message that bounced.
event_count: 4
related:
  lifecycle_optimizer_webhooks: https://products.zetaglobal.com/sailthru/Content/lo/using-lo/webhooks-lo.html