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

> ## Agent Instructions
> Every Lath operation is POST https://platform.trylath.com/<operation name with dots replaced by slashes>, with a JSON body and `Authorization: Bearer <key>`. `email.send` is POST /email/send.
> Branch on `error.code`, never on `error.message`. Every refusal also carries `error.fix`, which names the next step.
> Send an `Idempotency-Key` header on any operation that is not retry-safe, so a retry cannot run it twice.
> A `lath_test_` key emails only the account's own members and sends no SMS; a `lath_live_` key reaches real recipients and is billed.
> The OpenAPI document, generated from the same registry as the routes, is at https://platform.trylath.com/openapi.json.

# email.domain.returnPath.set

> Moves the domain's return path — the subdomain bounces return to, used as the envelope MAIL FROM so SPF aligns with your From — to another label, like send or bounces. The two return-path records move to the new host, so a verified domain goes back to pending until they resolve there: run email.domain.verify once they do. Mail from the domain keeps going out meanwhile; the sender is only told the new MAIL FROM after the records verify.



## OpenAPI

````yaml /api-reference/openapi.json post /email/domain/returnPath/set
openapi: 3.1.0
info:
  title: Lath API
  version: 0.1.0
  description: >-
    Every operation is one POST. The same set is reachable over MCP, the SDK and
    the CLI; nothing is dashboard-only.
servers:
  - url: https://platform.trylath.com
    description: This deployment
security: []
paths:
  /email/domain/returnPath/set:
    post:
      tags:
        - email
      summary: email.domain.returnPath.set
      description: >-
        Moves the domain's return path — the subdomain bounces return to, used
        as the envelope MAIL FROM so SPF aligns with your From — to another
        label, like send or bounces. The two return-path records move to the new
        host, so a verified domain goes back to pending until they resolve
        there: run email.domain.verify once they do. Mail from the domain keeps
        going out meanwhile; the sender is only told the new MAIL FROM after the
        records verify.
      operationId: email.domain.returnPath.set
      parameters:
        - name: Idempotency-Key
          in: header
          required: false
          schema:
            type: string
          description: >-
            Replays the stored response for the same key and input; refuses
            different input.
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $schema: https://json-schema.org/draft/2020-12/schema
              type: object
              properties:
                domainId:
                  type: string
                  format: uuid
                  pattern: >-
                    ^([0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[1-8][0-9a-fA-F]{3}-[89abAB][0-9a-fA-F]{3}-[0-9a-fA-F]{12}|00000000-0000-0000-0000-000000000000|ffffffff-ffff-ffff-ffff-ffffffffffff)$
                returnPath:
                  type: string
                  minLength: 1
                  maxLength: 63
                  description: 'One DNS label: "send" makes the return path send.<domain>.'
              required:
                - domainId
                - returnPath
              additionalProperties: false
      responses:
        '200':
          description: '{ activityId, result }. activityId is empty for reads.'
          content:
            application/json:
              schema:
                type: object
                properties:
                  activityId:
                    type: string
                    description: The activity this call created, or empty for a read.
                  result:
                    $schema: https://json-schema.org/draft/2020-12/schema
                    type: object
                    properties:
                      domain:
                        type: object
                        properties:
                          id:
                            type: string
                            format: uuid
                            pattern: >-
                              ^([0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[1-8][0-9a-fA-F]{3}-[89abAB][0-9a-fA-F]{3}-[0-9a-fA-F]{12}|00000000-0000-0000-0000-000000000000|ffffffff-ffff-ffff-ffff-ffffffffffff)$
                          domain:
                            type: string
                          status:
                            type: string
                            enum:
                              - pending
                              - verified
                              - failed
                          records:
                            type: array
                            items:
                              type: object
                              properties:
                                type:
                                  type: string
                                name:
                                  type: string
                                value:
                                  type: string
                              required:
                                - type
                                - name
                                - value
                              additionalProperties: {}
                          returnPath:
                            type: object
                            properties:
                              label:
                                type: string
                              host:
                                type: string
                              inUse:
                                type: boolean
                            required:
                              - label
                              - host
                              - inUse
                            additionalProperties: {}
                        required:
                          - id
                          - domain
                          - status
                          - records
                          - returnPath
                        additionalProperties: {}
                      changed:
                        type: boolean
                      next:
                        type: string
                    required:
                      - domain
                      - changed
                      - next
                    additionalProperties: {}
                required:
                  - activityId
                  - result
        '400':
          description: invalid_input or invalid_json
        '401':
          description: unauthenticated
        '403':
          description: forbidden
        '404':
          description: not_found
        '409':
          description: 'conflict: idempotency_mismatch, email_taken, last_key'
        '413':
          description: body_too_large
        '429':
          description: rate_limited
      security:
        - bearer: []
components:
  securitySchemes:
    bearer:
      type: http
      scheme: bearer
      description: >-
        A Lath API key: lath_live_sk… or lath_test_sk… on a server,
        lath_live_pk… or lath_test_pk… in a browser.

````