> ## Documentation Index > Fetch the complete documentation index at: https://docs.paubox.com/llms.txt > Use this file to discover all available pages before exploring further. # Send bulk messages > Sends multiple messages in one request. Paubox recommends batches of 50 or fewer. Source tracking IDs are returned in the same order as the messages array. ## OpenAPI ````yaml openapi1 POST /bulk_messages openapi: 3.0.0 info: title: Paubox Email API description: > Public documentation for Paubox's Transactional Email API ## Authentication **IMPORTANT**: This API uses a custom authentication format that requires the "Token token=" prefix. All requests must include the Authorization header in this exact format: ``` Authorization: Token token=YOUR_API_KEY ``` **Note for Code Generation Tools**: Auto-generated code from this specification may need to be modified to include the "Token token=" prefix, as most generators expect standard Bearer token format. version: 1.0.0 servers: - url: https://api.paubox.net/v1/{api_username} description: Paubox Email API variables: api_username: description: Your Paubox Email API endpoint username default: YOUR_API_USERNAME security: - PauboxToken: [] tags: - name: Messages description: Send individual or bulk transactional email - name: Dynamic Templates description: Manage and use dynamic Handlebars templates for email content paths: /bulk_messages: post: tags: - Messages summary: Send multiple email messages (batch) description: > Sends multiple messages in one request. Paubox recommends batches of 50 or fewer. Source tracking IDs are returned in the same order as the messages array. operationId: sendBulkMessages requestBody: content: application/json: schema: $ref: '#/components/schemas/BulkSendRequest' examples: twoMessages: summary: Two-message batch value: data: messages: - recipients: - recipient@host.com - Recipient Name bcc: - recipient3@host.com - Recipient Name headers: subject: sample email from: sender@authorized_domain.com reply-to: Sender Name x-custom-header: sample custom header content: text/plain: Hello World! text/html:

Hello World!

attachments: - fileName: hello_world.txt contentType: text/plain content: SGVsbG8gV29ybGQh allowNonTLS: false forceSecureNotification: false - recipients: - recipient2@host.com - Recipient Name headers: subject: sample email from: sender@authorized_domain.com reply-to: Sender Name content: text/plain: Hello World! text/html:

Hello World!

attachments: - fileName: hello_world.txt contentType: text/plain content: SGVsbG8gV29ybGQh required: true responses: '200': description: Batch accepted content: application/json: schema: $ref: '#/components/schemas/BulkSendResponse' examples: ok: value: messages: - sourceTrackingId: 3d38ab13-0af8-4028-bd45-999999999999 customHeaders: X-Custom-Header: value data: Service OK - sourceTrackingId: 3d38ab13-0af8-4028-bd45-000000000000 customHeaders: X-Custom-Header: value data: Service OK '400': description: Bad request content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' security: - PauboxToken: [] components: schemas: BulkSendRequest: required: - data type: object properties: data: $ref: '#/components/schemas/BulkSendRequest_data' BulkSendResponse: type: object properties: messages: type: array items: $ref: '#/components/schemas/BulkSendResponse_messages' ErrorResponse: type: object properties: errors: type: array items: $ref: '#/components/schemas/ErrorResponse_errors' BulkSendRequest_data: required: - messages type: object properties: messages: type: array description: Recommended 50 or fewer per request. items: $ref: '#/components/schemas/Message' BulkSendResponse_messages: type: object properties: sourceTrackingId: type: string customHeaders: type: object additionalProperties: type: string data: type: string example: Service OK ErrorResponse_errors: type: object properties: code: type: integer title: type: string details: type: string Message: required: - content - headers - recipients type: object properties: recipients: minItems: 1 type: array items: type: string description: >- Email address, optionally with display name (e.g., "J. Smith "). bcc: type: array items: type: string cc: type: array items: type: string headers: $ref: '#/components/schemas/MessageHeaders' allowNonTLS: type: boolean description: > Allow delivery over non-TLS rather than converting to a Secure Portal message. Not HIPAA-compliant if the message contains PHI. default: false forceSecureNotification: type: boolean description: > Force delivery as a Paubox Secure Message; recipient gets a pickup notification with a link. default: false content: $ref: '#/components/schemas/MessageContent' attachments: type: array items: $ref: '#/components/schemas/Attachment' MessageHeaders: required: - from - subject type: object properties: subject: type: string from: type: string description: Must match the verified domain of your API key. reply-to: type: string description: >- Reply-to address; must match a verified domain if different from from. List-Unsubscribe: type: string description: > Insert a List-Unsubscribe header (mailto and/or http). See RFC guidance for syntax. List-Unsubscribe-Post: type: string description: Used in conjunction with List-Unsubscribe header. x-custom-header: type: string description: >- Example custom header; any custom header may be added with an X- prefix. additionalProperties: type: string description: Any additional X- prefixed custom header values. MessageContent: type: object properties: text/plain: type: string description: Plain text message body. Required if text/html is not provided. text/html: type: string description: > HTML message body. May be HTML-escaped, base64-encoded, or a valid unescaped string. CSS in