--- description: Send emails directly from Cloudflare Workers using the Email Service binding and send() method. title: Workers API image: https://developers.cloudflare.com/og-docs.png --- [Skip to content](#main-content) > Documentation Index > Fetch the complete documentation index at: https://developers.cloudflare.com/email-service/llms.txt > Use this file to discover all available pages before exploring further. # Workers API Last updated Aug 24, 2026|Copy as Markdown|[View as Markdown](https://e8aee267.previews.developers.cloudflare.com/email-service/api/send-emails/workers-api/index.md)|[Agent setup](https://e8aee267.previews.developers.cloudflare.com/agent-setup/) The Workers API provides native email sending capabilities directly from your Cloudflare Workers through bindings. If you are not using Workers, you can send emails using the [REST API](https://e8aee267.previews.developers.cloudflare.com/email-service/api/send-emails/rest-api/) instead. ## Email binding Configure a `send_email` binding in your Wrangler configuration file to enable email sending: ```jsonc { "send_email": [{ "name": "EMAIL" }], } ``` ```toml [[send_email]] name = "EMAIL" ``` You can restrict which senders and recipients a binding may use. Refer to [Configure send bindings](https://e8aee267.previews.developers.cloudflare.com/email-service/configuration/send-bindings/) for the available restriction attributes and examples. ## `send()` method Send a single email using the `send()` method on your email binding. ### Interface ```ts interface SendEmail { send(message: EmailMessage | EmailMessageBuilder): Promise; } interface EmailAddress { email: string; name?: string; } // Structured email builder (recommended) interface EmailMessageBuilder { to: string | EmailAddress | (string | EmailAddress)[]; // Max 50 recipients from: string | EmailAddress; subject: string; html?: string; text?: string; cc?: string | EmailAddress | (string | EmailAddress)[]; bcc?: string | EmailAddress | (string | EmailAddress)[]; replyTo?: string | EmailAddress; attachments?: Attachment[]; // Custom headers. See /email-service/reference/headers/ headers?: { [key: string]: string }; // The combined number of addresses in `to`, `cc`, and `bcc` must not // exceed 50. See /email-service/platform/limits/ for all limits. } interface Attachment { content: string | ArrayBuffer | ArrayBufferView; // Base64 string or binary content filename: string; type: string; // MIME type disposition: "attachment" | "inline"; contentId?: string; // For inline attachments } interface EmailSendResult { messageId: string; // Unique email ID } // Errors are thrown as standard Error objects with a `code` property // try { await env.EMAIL.send(...) } catch (e) { console.log(e.code, e.message) } ``` Local development with binary attachments When using `wrangler dev` without [remote bindings](https://e8aee267.previews.developers.cloudflare.com/workers/local-development/#remote-bindings), `ArrayBuffer` and `ArrayBufferView` content in attachments cannot be serialized by the local simulator. Refer to [local development for email sending](https://e8aee267.previews.developers.cloudflare.com/email-service/local-development/sending/#known-limitations). ### Basic usage ```ts const response = await env.EMAIL.send({ to: "recipient@example.com", from: "welcome@yourdomain.com", subject: "Welcome to our service!", html: "

Welcome!

Thanks for signing up.

", text: "Welcome! Thanks for signing up.", }); ``` For multiple recipients, CC/BCC, and named addresses, see [Specify recipients](https://e8aee267.previews.developers.cloudflare.com/email-service/examples/email-sending/recipients/). ### Attachments Send files by including base64-encoded content in the `attachments` array. The total message size must not exceed 5 MiB (including attachments). ```ts const response = await env.EMAIL.send({ to: "customer@example.com", from: "invoices@yourdomain.com", subject: "Your Invoice", html: "

Invoice attached

Please find your invoice attached.

", attachments: [ { content: "JVBERi0xLjQKJeLjz9MKMSAwIG9iag...", // Base64 PDF content filename: "invoice-12345.pdf", type: "application/pdf", disposition: "attachment", }, ], }); ``` For inline images and file uploads, see [Email attachments](https://e8aee267.previews.developers.cloudflare.com/email-service/examples/email-sending/email-attachments/). ## Error handling Handle email sending errors gracefully: ```ts export default { async fetch(request: Request, env: Env): Promise { try { const response = await env.EMAIL.send({ to: "user@example.com", from: "noreply@yourdomain.com", subject: "Test Email", text: "This is a test email.", }); return new Response( JSON.stringify({ success: true, emailId: response.messageId, }), ); } catch (error) { // Error has .code and .message properties console.error("Email sending failed:", error.code, error.message); // Handle specific error types switch (error.code) { case "E_SENDER_NOT_VERIFIED": return new Response( JSON.stringify({ success: false, error: "Please verify your sender domain first", }), { status: 400 }, ); case "E_RATE_LIMIT_EXCEEDED": return new Response( JSON.stringify({ success: false, error: "Rate limit exceeded. Please try again later", }), { status: 429 }, ); default: return new Response( JSON.stringify({ success: false, error: error.message, }), { status: 500 }, ); } } }, }; ``` ## Error codes The following error codes may be returned when sending emails: | Error Code | Description | Common Causes | | --------------------------------- | ----------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------- | | E\_VALIDATION\_ERROR | Validation error in the payload | Invalid email format, missing required fields, malformed data | | E\_FIELD\_MISSING | Required field is missing | Missing to, from, or subject fields | | E\_TOO\_MANY\_RECIPIENTS | Too many recipients in to/cc/bcc arrays | Combined recipients exceed 50 limit | | E\_TOO\_MANY\_ATTACHMENTS | Too many attachments in attachments array | attachments array exceeds 32 entries | | E\_SENDER\_NOT\_VERIFIED | Sender domain not verified | Attempting to send from unverified domain | | E\_RECIPIENT\_NOT\_ALLOWED | Recipient not in allowed list | Recipient address not in allowed\_destination\_addresses | | E\_RECIPIENT\_SUPPRESSED | Recipient is on suppression list | Email address has bounced or reported your emails as spam | | E\_SENDER\_DOMAIN\_NOT\_AVAILABLE | Domain not available for sending | Domain not onboarded to Email Service | | E\_CONTENT\_TOO\_LARGE | Email content exceeds size limit | Total message size exceeds the maximum | | E\_DELIVERY\_FAILED | Could not deliver the email | SMTP delivery failure, recipient server rejection | | E\_RATE\_LIMIT\_EXCEEDED | Rate limit exceeded | Sending rate limit reached | | E\_DAILY\_LIMIT\_EXCEEDED | Daily limit exceeded | Daily sending quota reached | | E\_INTERNAL\_SERVER\_ERROR | Internal service error | Email Service temporarily unavailable | | E\_HEADER\_NOT\_ALLOWED | Header not allowed | Header is platform-controlled or not on the [allowlist](https://e8aee267.previews.developers.cloudflare.com/email-service/reference/headers/) | | E\_HEADER\_USE\_API\_FIELD | Must use API field | Header like From must be set via the dedicated API field | | E\_HEADER\_VALUE\_INVALID | Header value invalid | Malformed value, empty, or incorrect format | | E\_HEADER\_VALUE\_TOO\_LONG | Header value too long | Value exceeds 2,048 byte limit | | E\_HEADER\_NAME\_INVALID | Header name invalid | Invalid characters or exceeds 100 byte limit | | E\_HEADERS\_TOO\_LARGE | Headers payload too large | Total custom headers exceed 16 KB limit | | E\_HEADERS\_TOO\_MANY | Too many headers | More than 20 allowlisted (non-X) custom headers | ## Legacy `EmailMessage` API The `EmailMessage` API remains supported for backward compatibility. Use it when you already have a raw [RFC 5322 ↗](https://datatracker.ietf.org/doc/html/rfc5322) MIME message to send. For new code, prefer the structured [send() method](#send-method) above. ```ts import { EmailMessage } from "cloudflare:email"; import { createMimeMessage } from "mimetext"; export default { async fetch(request: Request, env: Env): Promise { const msg = createMimeMessage(); msg.setSender({ name: "Sender", addr: "sender@yourdomain.com" }); msg.setRecipient("recipient@example.com"); msg.setSubject("Legacy Email"); msg.addMessage({ contentType: "text/html", data: "

Hello from legacy API

", }); const message = new EmailMessage( "sender@yourdomain.com", "recipient@example.com", msg.asRaw(), ); await env.EMAIL.send(message); return new Response("Legacy email sent"); }, }; ``` --- ## Next steps * See the [REST API](https://e8aee267.previews.developers.cloudflare.com/email-service/api/send-emails/rest-api/) for sending emails without Workers * See [SMTP](https://e8aee267.previews.developers.cloudflare.com/email-service/api/send-emails/smtp/) for sending from any SMTP-capable application or mail client * See [practical examples](https://e8aee267.previews.developers.cloudflare.com/email-service/examples/) of email sending patterns * Learn about [email routing](https://e8aee267.previews.developers.cloudflare.com/email-service/api/route-emails/) for handling incoming emails * Explore [email authentication](https://e8aee267.previews.developers.cloudflare.com/email-service/concepts/email-authentication/) for better deliverability Was this helpful? YesNo ## On this page [![](https://e8aee267.previews.developers.cloudflare.com/_astro/logo.te5VL_aD.svg)Docs](https://e8aee267.previews.developers.cloudflare.com/) ```json {"@context":"https://schema.org","@type":"TechArticle","@id":"https://developers.cloudflare.com/email-service/api/send-emails/workers-api/#page","headline":"Workers API · Cloudflare Email Service docs","description":"Send emails directly from Cloudflare Workers using the Email Service binding and send() method.","url":"https://developers.cloudflare.com/email-service/api/send-emails/workers-api/","inLanguage":"en","image":"https://developers.cloudflare.com/og-docs.png","dateModified":"2026-08-24","publisher":{"@type":"Organization","name":"Cloudflare","url":"https://www.cloudflare.com/"},"isPartOf":{"@type":"WebSite","@id":"https://developers.cloudflare.com/#website","name":"Cloudflare Docs","url":"https://developers.cloudflare.com/"}} ```