find_apisBrowse and filter every API in the catalog.
get_api_artifactsOne API's artifacts, grouped by type.
get_openapiThe primary OpenAPI for this API.
find_similar_apisAPIs that look like this one.
apis_io_searchSTART HERE — APIs, providers and tags for one query, each with its total.
resolveTurn a domain, URL or GitHub org into the provider it belongs to.
find_cohortsEvery scored population of providers in the catalog.

All 92 tools →

Call it yourself

curl for this page

This API

curl "https://apis.io/api/v1/apis/mailsenpai:mailsenpai-sending-api"

All apis

curl "https://apis.io/api/v1/apis?limit=25"

Calls without X-API-Key need no key. Calls with it need a paid plan — get a key.

Get an API key

Free tier, no form to fill in. Signing in shares your email address with us — we store it to create your key and to recognise you if you sign in with another provider. See our Privacy Policy and Terms.

GitHub Google LinkedIn

A second provider on the same verified email joins the account you already have.

OpenAPI Specification

openapi: 3.2.0
info:
  title: SMTP Senpai Sending API
  version: 1.1.0
  summary: Transactional email sending, log, suppression list and website forms.
  description: 'REST API of SMTP Senpai, the MailSenpai relay. Every response is JSON with an `ok` field; on errors there is also `errore`, with an Italian message. You find the key in the customer area, SMTP Senpai page. Call it from your server: the API does not accept browser requests (no CORS), except the form endpoint.'
  contact:
    name: MailSenpai
    url: https://en.mailsenpai.com/smtp-api/
servers:
- url: https://app.mailsenpai.com/relay/v1
security:
- chiaveBearer: []
tags:
- name: Sending
paths:
  /invio:
    post:
      operationId: invio
      tags:
      - Sending
      summary: Send an email to one or more recipients
      description: 'Up to 50 recipients per call, each with their own copy; attachments up to 10 files and 10 MB. CC and BCC only over SMTP. The sender must be on a verified domain. Suppressed recipients are held (`dropped` event). With the `Idempotency-Key` header the same request repeated within 24 hours returns the first response (with `Idempotent-Replayed: true`) without sending again.'
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/InvioRichiesta'
            examples:
              italiano:
                summary: Italian field names
                value:
                  a: cliente@esempio.it
                  da: ordini@tuodominio.it
                  nome_mittente: Il tuo negozio
                  oggetto: Conferma ordine 10293
                  html: <p>Grazie, il tuo ordine è confermato.</p>
                  rispondi_a: assistenza@tuodominio.it
                  intestazioni:
                    X-Ordine: '10293'
              inglese:
                summary: English aliases
                value:
                  to: customer@example.com
                  from: orders@yourdomain.com
                  from_name: Your shop
                  subject: Order 10293 confirmed
                  text: Thanks, your order is confirmed.
          application/x-www-form-urlencoded:
            schema:
              $ref: '#/components/schemas/InvioRichiesta'
      responses:
        '200':
          description: Accepted, or held because the recipient is suppressed.
          content:
            application/json:
              schema:
                oneOf:
                - $ref: '#/components/schemas/InvioOk'
                - $ref: '#/components/schemas/InvioSoppresso'
                - $ref: '#/components/schemas/InvioMulti'
              examples:
                inviata:
                  value:
                    ok: true
                    inviato: true
                    id_messaggio: 9f2c4e1a7b3d5f6e8a9b0c1d@tuodominio.it
                    residuo: 8759
                    oltre_il_piano: false
                soppressa:
                  value:
                    ok: true
                    inviato: false
                    motivo: indirizzo nella lista di soppressione
          headers:
            Idempotent-Replayed:
              schema:
                type: string
                const: 'true'
              description: Present when the response is the stored one of an identical request.
        '400':
          description: Missing or invalid data.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Errore'
              example:
                ok: false
                errore: destinatario non valido
        '401':
          $ref: '#/components/responses/ChiaveNonValida'
        '403':
          description: Sender on an unverified domain, or account suspended.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Errore'
              example:
                ok: false
                errore: il dominio esempio.com non risulta fra quelli verificati per il tuo account
        '429':
          description: Monthly volume used up and sending continuity off (or spending cap reached).
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ErroreVolume'
              example:
                ok: false
                errore: 'volume del mese esaurito: aumenta il piano o accendi la continuità di invio dalla tua area'
                residuo: 0
                aumenta: https://app.mailsenpai.com/customer/il-mio-piano
                pannello: https://app.mailsenpai.com/customer/relay-smtp
        '502':
          description: 'The sending server did not accept the message or could not be reached: the text reports the reply received.'
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Errore'
              example:
                ok: false
                errore: 'il server di invio ha risposto: 451 4.3.0 errore temporaneo'
        '405':
          description: 'HTTP method not allowed: the Allow header gives the right one.'
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Errore'
              example:
                ok: false
                errore: 'metodo non ammesso: usa GET'
        '409':
          description: A request with the same Idempotency-Key is still in progress.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Errore'
              example:
                ok: false
                errore: una richiesta con la stessa Idempotency-Key è ancora in corso
        '413':
          description: Attachments over 10 MB.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Errore'
              example:
                ok: false
                errore: 'allegati troppo grandi: al massimo 10 MB in tutto'
        '422':
          description: Idempotency-Key already used with different data.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Errore'
              example:
                ok: false
                errore: questa Idempotency-Key è già stata usata nelle ultime 24 ore con dati diversi
      parameters:
      - name: Idempotency-Key
        in: header
        required: false
        schema:
          type: string
          maxLength: 100
          pattern: ^[\x21-\x7E]+$
        description: Your own key (for example the order id), valid for 24 hours.
components:
  schemas:
    InvioSoppresso:
      type: object
      required:
      - ok
      - inviato
      - motivo
      properties:
        ok:
          type: boolean
          const: true
        inviato:
          type: boolean
          const: false
        motivo:
          type: string
          example: indirizzo nella lista di soppressione
    InvioOk:
      type: object
      required:
      - ok
      - inviato
      - id_messaggio
      properties:
        ok:
          type: boolean
          const: true
        inviato:
          type: boolean
          const: true
        id_messaggio:
          type: string
          description: Identifier given to the message; it is also its Message-ID (without angle brackets).
          example: 9f2c4e1a7b3d5f6e8a9b0c1d@tuodominio.it
        residuo:
          type: integer
          description: Estimate of the volume left this month.
        oltre_il_piano:
          type: boolean
          description: True if the included volume was used up and the email went out thanks to sending continuity.
    Allegato:
      type: object
      required:
      - nome
      - contenuto
      properties:
        nome:
          type: string
          maxLength: 150
          description: 'File name. Alias: `filename`. Executable files (.exe, .js, .bat…) are refused.'
        contenuto:
          type: string
          contentEncoding: base64
          description: 'Base64 content. Alias: `content`.'
        tipo:
          type: string
          description: 'MIME type, for example application/pdf. Alias: `content_type`. Default: application/octet-stream.'
    InvioMulti:
      type: object
      required:
      - ok
      - inviati
      - risultati
      description: Response when `a` is a list.
      properties:
        ok:
          type: boolean
          const: true
        inviati:
          type: integer
        non_inviati:
          type: integer
        risultati:
          type: array
          items:
            type: object
            properties:
              a:
                type: string
              inviato:
                type: boolean
              id_messaggio:
                type: string
              motivo:
                type: string
                description: Why it was not sent (suppression).
              errore:
                type: string
                description: Sending server error or volume used up for that recipient.
        residuo:
          type: integer
        oltre_il_piano:
          type: boolean
    ErroreVolume:
      allOf:
      - $ref: '#/components/schemas/Errore'
      - type: object
        properties:
          residuo:
            type: integer
            const: 0
          aumenta:
            type: string
            format: uri
            description: Customer-area page where you can raise the volume.
          pannello:
            type: string
            format: uri
            description: Customer-area page with usage and sending continuity.
    Errore:
      type: object
      required:
      - ok
      - errore
      properties:
        ok:
          type: boolean
          const: false
        errore:
          type: string
          description: Human-readable explanation, always in Italian.
    InvioRichiesta:
      type: object
      description: 'One or more recipients (up to 50): each one gets their own copy. Italian names take precedence over the English aliases if you send both.'
      properties:
        a:
          oneOf:
          - type: string
            format: email
          - type: array
            items:
              type: string
              format: email
            minItems: 1
            maxItems: 50
          description: Recipient, or a list of up to 50 recipients.
        to:
          oneOf:
          - type: string
            format: email
          - type: array
            items:
              type: string
              format: email
            minItems: 1
            maxItems: 50
          description: Alias of `a`.
        da:
          type: string
          format: email
          description: 'Sender: must be on a verified domain of your account (subdomains are accepted).'
        from:
          type: string
          format: email
          description: Alias of `da`.
        nome_mittente:
          type: string
          description: Sender display name.
        from_name:
          type: string
          description: Alias of `nome_mittente`.
        oggetto:
          type: string
          minLength: 1
        subject:
          type: string
          description: Alias of `oggetto`.
        html:
          type: string
          description: HTML body. If the text part is missing, it is derived from the HTML.
        testo:
          type: string
          description: Plain-text body.
        text:
          type: string
          description: Alias of `testo`.
        rispondi_a:
          type: string
          format: email
          description: Reply-To address. Ignored if it is not a valid address.
        reply_to:
          type: string
          format: email
          description: Alias of `rispondi_a`.
        intestazioni:
          type: object
          additionalProperties:
            type: string
          description: Custom headers. Only `X-…` names pass (letters, digits and hyphens, max 40 characters after `X-`); others are dropped silently.
          example:
            X-Ordine: A-10293
        headers:
          type: object
          additionalProperties:
            type: string
          description: Alias of `intestazioni`.
        allegati:
          type: array
          maxItems: 10
          items:
            $ref: '#/components/schemas/Allegato'
          description: Up to 10 files and 10 MB in total (after decoding).
        attachments:
          type: array
          maxItems: 10
          items:
            $ref: '#/components/schemas/Allegato'
          description: Alias of `allegati`.
      allOf:
      - anyOf:
        - required:
          - a
        - required:
          - to
      - anyOf:
        - required:
          - da
        - required:
          - from
      - anyOf:
        - required:
          - oggetto
        - required:
          - subject
      - anyOf:
        - required:
          - html
        - required:
          - testo
        - required:
          - text
  responses:
    ChiaveNonValida:
      description: Missing or invalid key.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Errore'
          example:
            ok: false
            errore: chiave non valida
  securitySchemes:
    chiaveBearer:
      type: http
      scheme: bearer
      bearerFormat: msp_…
      description: '`Authorization: Bearer msp_…` (the key starts with `msp_`). As an alternative the `chiave` field is accepted in the body (JSON or form). A key in the URL (`?chiave=`) is refused with 401: it would end up in logs.'
externalDocs:
  description: Documentation with examples
  url: https://en.mailsenpai.com/smtp-api/