> ## Documentation Index
> Fetch the complete documentation index at: https://sendmux.ai/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Get a mailbox thread

> Returns thread metadata, message IDs, participants, last message, unread count, and state for one conversation. Responses include a weak `ETag` header.



## OpenAPI

````yaml /openapi-app.json get /mailbox/threads/{thread_id}
openapi: 3.1.0
info:
  description: Programmatic access to your Sendmux email infrastructure.
  title: Sendmux API
  version: 1.0.0
servers:
  - description: API v1
    url: https://app.sendmux.ai/api/v1
security:
  - bearerAuth: []
paths:
  /mailbox/threads/{thread_id}:
    get:
      tags:
        - Mailbox API
      summary: Get a mailbox thread
      description: >-
        Returns thread metadata, message IDs, participants, last message, unread
        count, and state for one conversation. Responses include a weak `ETag`
        header.
      operationId: mailboxGetThread
      parameters:
        - in: path
          name: thread_id
          required: true
          schema:
            description: Thread ID.
            type: string
        - in: header
          name: If-None-Match
          required: false
          schema:
            description: Weak ETag from a previous response. Returns 304 when unchanged.
            type: string
        - description: >-
            Mailbox public ID to target when the credential grants access to
            more than one mailbox. Omit when the credential is scoped to exactly
            one mailbox.
          in: query
          name: mailbox_id
          required: false
          schema:
            type: string
      responses:
        '200':
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/MailboxThreadDetailResponse'
          description: Thread
        '304':
          description: Not modified
        '404':
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ApiError'
          description: Thread not found
      security:
        - bearerAuth: []
components:
  schemas:
    MailboxThreadDetailResponse:
      allOf:
        - $ref: '#/components/schemas/SuccessEnvelope'
        - properties:
            data:
              $ref: '#/components/schemas/MailboxThread'
            meta:
              $ref: '#/components/schemas/ResponseMeta'
          required:
            - data
          type: object
      unevaluatedProperties: false
    ApiError:
      additionalProperties: false
      properties:
        error:
          additionalProperties: false
          properties:
            code:
              description: Machine-readable error code
              enum:
                - invalid_parameter
                - missing_parameter
                - authentication_required
                - insufficient_permissions
                - not_found
                - conflict
                - limit_exceeded
                - idempotency_conflict
                - payload_too_large
                - validation_error
                - rate_limit_exceeded
                - service_unavailable
                - internal_error
              example: invalid_parameter
              type: string
            doc_url:
              description: Link to relevant documentation
              type: string
            errors:
              description: >-
                Accumulated per-field issues for validation errors. Only present
                on 400/422 responses.
              items:
                $ref: '#/components/schemas/ApiErrorDetail'
              type: array
            message:
              description: Human-readable error description
              type: string
            param:
              description: The parameter that caused the error
              type: string
            retryable:
              description: >-
                Whether the caller may safely retry this request. 4xx are
                typically false (except 429); 5xx are typically true.
              example: false
              type: boolean
          required:
            - code
            - message
            - retryable
          type: object
        meta:
          additionalProperties: false
          properties:
            request_id:
              example: req_clxxxxxxxxxxxxxxxxxxxxxxxxx
              type: string
          required:
            - request_id
          type: object
        ok:
          enum:
            - false
          type: boolean
      required:
        - ok
        - error
        - meta
      type: object
    SuccessEnvelope:
      properties:
        meta:
          additionalProperties: {}
          properties: {}
          type: object
        ok:
          enum:
            - true
          type: boolean
      required:
        - ok
        - meta
      type: object
    MailboxThread:
      allOf:
        - $ref: '#/components/schemas/MailboxThreadSummary'
        - additionalProperties: false
          properties:
            message_ids:
              items:
                type: string
              type: array
          required:
            - message_ids
          type: object
    ResponseMeta:
      additionalProperties: false
      properties:
        request_id:
          example: req_clxxxxxxxxxxxxxxxxxxxxxxxxx
          type: string
      required:
        - request_id
      type: object
    ApiErrorDetail:
      additionalProperties: false
      properties:
        code:
          description: >-
            Machine-readable issue code from the validator (e.g. zod issue
            code).
          example: invalid_string
          type: string
        field:
          description: Dot-path of the offending request field.
          example: recipient.email
          type: string
        message:
          description: Human-readable issue description.
          type: string
      required:
        - field
        - code
        - message
      type: object
    MailboxThreadSummary:
      additionalProperties: false
      properties:
        folder_ids:
          items:
            type: string
          type: array
        has_attachments:
          type: boolean
        id:
          description: Thread ID
          type: string
        last_message:
          allOf:
            - $ref: '#/components/schemas/MailboxMessageSummary'
            - type:
                - object
                - 'null'
        message_count:
          type: integer
        participants:
          items:
            $ref: '#/components/schemas/MailboxAddress'
          type: array
        states:
          additionalProperties: false
          properties:
            email_state:
              type:
                - string
                - 'null'
            thread_state:
              type:
                - string
                - 'null'
          required:
            - thread_state
            - email_state
          type: object
        subject:
          type:
            - string
            - 'null'
        unread_count:
          type: integer
      required:
        - id
        - subject
        - message_count
        - unread_count
        - has_attachments
        - folder_ids
        - participants
        - last_message
        - states
      type: object
    MailboxMessageSummary:
      additionalProperties: false
      properties:
        attachments:
          description: >-
            Attachment metadata for this message. Each item includes a
            short-lived `download_url`; if it expires, fetch message metadata
            again.
          items:
            $ref: '#/components/schemas/MailboxAttachment'
          type: array
        bcc:
          items:
            $ref: '#/components/schemas/MailboxAddress'
          type: array
        cc:
          items:
            $ref: '#/components/schemas/MailboxAddress'
          type: array
        flags:
          $ref: '#/components/schemas/MailboxMessageFlags'
        folder_ids:
          items:
            type: string
          type: array
        from:
          allOf:
            - $ref: '#/components/schemas/MailboxAddress'
            - type:
                - object
                - 'null'
        has_attachments:
          type: boolean
        id:
          description: Message ID
          type: string
        keywords:
          description: Active message keywords, including system flags and custom labels.
          example:
            - $seen
            - $flagged
            - agent_triaged
          items:
            type: string
          type: array
        preview:
          type:
            - string
            - 'null'
        received_at:
          type:
            - string
            - 'null'
        sent_at:
          type:
            - string
            - 'null'
        size_bytes:
          type:
            - integer
            - 'null'
        subject:
          type:
            - string
            - 'null'
        thread_id:
          type:
            - string
            - 'null'
        to:
          items:
            $ref: '#/components/schemas/MailboxAddress'
          type: array
      required:
        - id
        - thread_id
        - folder_ids
        - subject
        - preview
        - from
        - to
        - cc
        - bcc
        - received_at
        - sent_at
        - size_bytes
        - has_attachments
        - keywords
        - flags
      type: object
    MailboxAddress:
      additionalProperties: false
      properties:
        email:
          example: agent@example.com
          format: email
          type: string
        name:
          example: Support
          type:
            - string
            - 'null'
      required:
        - email
        - name
      type: object
    MailboxAttachment:
      additionalProperties: false
      properties:
        content_id:
          description: Content ID for inline attachments, when present.
          type:
            - string
            - 'null'
        content_type:
          example: application/pdf
          type: string
        disposition:
          example: attachment
          type:
            - string
            - 'null'
        download_url:
          description: >-
            Short-lived URL for this exact attachment. Fetch it promptly; if it
            expires, call the message or attachment metadata endpoint again to
            receive a fresh URL.
          example: >-
            https://app.sendmux.ai/api/v1/mailbox/messages/msg_123/attachment-downloads/attref_abc123?download_token=...
          type: string
        filename:
          example: invoice.pdf
          type:
            - string
            - 'null'
        id:
          description: Attachment blob ID.
          type: string
        size_bytes:
          example: 12345
          type:
            - integer
            - 'null'
      required:
        - id
        - filename
        - content_type
        - size_bytes
        - disposition
        - content_id
      type: object
    MailboxMessageFlags:
      additionalProperties: false
      properties:
        answered:
          type: boolean
        draft:
          type: boolean
        flagged:
          type: boolean
        seen:
          type: boolean
      required:
        - seen
        - flagged
        - draft
        - answered
      type: object
  securitySchemes:
    bearerAuth:
      bearerFormat: API Key
      description: >-
        Sendmux API key. Use a root API key for Management API routes, or a
        mailbox credential for Mailbox API routes. Obtain keys from the
        dashboard under API Keys.
      scheme: bearer
      type: http

````