> ## Documentation Index > Fetch the complete documentation index at: https://docs.openmail.sh/llms.txt > Use this file to discover all available pages before exploring further. # Send email > Send an email from an inbox. Requires Idempotency-Key header. Use threadId to reply to an existing thread. When replying on a thread where your inbox was CC'd (deliveryRole cc), the original sender is automatically CC'd. ## OpenAPI ````yaml /api-reference/openapi.json post /v1/inboxes/{id}/send openapi: 3.0.3 info: title: OpenMail API description: >- Email infrastructure API for AI agents. Create inboxes, send and receive email, and get real-time notifications via webhooks. version: 1.0.0 license: name: Proprietary servers: - url: https://api.openmail.sh security: - bearerAuth: [] tags: - name: pods description: Isolated sub-accounts for your end users or tenants - name: inboxes description: Email inboxes and their webhook configuration - name: messages description: Sending and listing messages - name: threads description: Conversation threads and read status - name: attachments description: Downloading and extracting text from attachments paths: /v1/inboxes/{id}/send: post: tags: - messages summary: Send email description: >- Send an email from an inbox. Requires Idempotency-Key header. Use threadId to reply to an existing thread. When replying on a thread where your inbox was CC'd (deliveryRole cc), the original sender is automatically CC'd. operationId: sendEmail parameters: - schema: type: string in: path name: id required: true - schema: type: string in: header name: idempotency-key required: false description: Unique key for idempotent sends (e.g. UUID) requestBody: required: true content: application/json: schema: type: object required: - to - body properties: to: type: string format: email subject: type: string minLength: 1 maxLength: 998 description: >- Required for new threads. Optional when threadId is set — the thread subject is used automatically (with Re: prefix). body: type: string minLength: 1 maxLength: 100000 description: >- Email body. Plain text or HTML — HTML is auto-detected and rendered, with a plain-text fallback generated automatically. bodyHtml: type: string maxLength: 500000 description: >- Provide only when the plain-text and HTML versions must differ. Omit for normal sends — put HTML in `body` instead. threadId: type: string description: Thread ID for replies includeQuote: type: boolean description: >- When replying with threadId, append a quoted copy of the previous message to the body. Defaults to true. Set false to send only your reply text. replyTo: type: string format: email description: >- Optional. Address that replies should be routed to (set as the `Reply-To` MIME header). Free plan: must be the address of an inbox you own in OpenMail. Pro plan or higher: any valid email address. cc: type: array items: type: string format: email description: Optional CC recipients. multipart/form-data: schema: type: object required: - to - body properties: to: type: string format: email subject: type: string minLength: 1 maxLength: 998 description: >- Required for new threads. Optional when threadId is set — the thread subject is used automatically (with Re: prefix). body: type: string minLength: 1 maxLength: 100000 description: >- Email body. Plain text or HTML — HTML is auto-detected and rendered, with a plain-text fallback generated automatically. bodyHtml: type: string maxLength: 500000 description: >- Provide only when the plain-text and HTML versions must differ. Omit for normal sends — put HTML in `body` instead. threadId: type: string description: Thread ID for replies includeQuote: type: boolean description: >- When replying with threadId, append a quoted copy of the previous message to the body. Defaults to true. Set false to send only your reply text. replyTo: type: string format: email description: >- Optional. Address that replies should be routed to (set as the `Reply-To` MIME header). Free plan: must be the address of an inbox you own in OpenMail. Pro plan or higher: any valid email address. cc: type: array items: type: string format: email description: Optional CC recipients. attachments: type: array items: type: string format: binary description: File attachments (max 25 MB total per email) responses: '200': description: Email sent (or idempotent replay) content: application/json: schema: description: Email sent (or idempotent replay) type: object additionalProperties: true properties: messageId: type: string threadId: type: string providerMessageId: type: string status: type: string enum: - pending - sent - failed '400': description: >- Missing Idempotency-Key, missing request body, invalid 'to'/'replyTo'/'cc' address, or missing subject when required content: application/json: schema: description: >- Missing Idempotency-Key, missing request body, invalid 'to'/'replyTo'/'cc' address, or missing subject when required allOf: - $ref: '#/components/schemas/Error' '402': description: >- Sending is paused because this account's monthly spend limit was reached (`spend_cap_paused`) content: application/json: schema: description: >- Sending is paused because this account's monthly spend limit was reached (`spend_cap_paused`) allOf: - $ref: '#/components/schemas/Error' '403': description: >- Feature requires a paid plan. Returned when a free-plan customer sets `replyTo` to an address that is not one of their own OpenMail inboxes (`feature_requires_paid_plan`), the account is banned (`account_banned`), or sending is suspended due to deliverability/abuse signals (`reputation_suspended`). content: application/json: schema: description: >- Feature requires a paid plan. Returned when a free-plan customer sets `replyTo` to an address that is not one of their own OpenMail inboxes (`feature_requires_paid_plan`), the account is banned (`account_banned`), or sending is suspended due to deliverability/abuse signals (`reputation_suspended`). allOf: - $ref: '#/components/schemas/Error' '404': description: Inbox or thread not found content: application/json: schema: description: Inbox or thread not found allOf: - $ref: '#/components/schemas/Error' '422': description: >- Content blocked (`unsafe_content`, `phishing_detected`), recipient domain has no MX records (`no_mx_records`), recipient suppressed for bounce/complaint (`recipient_suppressed`), or account storage limit exceeded (`storage_limit_exceeded`) content: application/json: schema: description: >- Content blocked (`unsafe_content`, `phishing_detected`), recipient domain has no MX records (`no_mx_records`), recipient suppressed for bounce/complaint (`recipient_suppressed`), or account storage limit exceeded (`storage_limit_exceeded`) allOf: - $ref: '#/components/schemas/Error' '429': description: >- Rate limit exceeded (global daily, per-inbox daily, per-inbox burst) or cold outreach limit. Check the Retry-After response header. content: application/json: schema: description: >- Rate limit exceeded (global daily, per-inbox daily, per-inbox burst) or cold outreach limit. Check the Retry-After response header. allOf: - $ref: '#/components/schemas/Error' components: schemas: Error: type: object additionalProperties: true properties: error: type: string message: type: string securitySchemes: bearerAuth: type: http scheme: bearer bearerFormat: API key ````