`hono-email/smtp` provides a connector-based SMTP sender. You choose a runtime connector, instantiate `SmtpTransport`, and pass it to `sendEmail()`. ## Example ```tsx import CloudflareConnector from 'hono-email/smtp/cloudflare' import { Body, Html, Text, sendEmail } from 'hono-email' import { SmtpTransport } from 'hono-email/smtp' const dkimPrivateKey = `-----BEGIN PRIVATE KEY----- ... -----END PRIVATE KEY-----` const smtp = new SmtpTransport({ connector: CloudflareConnector, hostname: 'smtp.example.com', port: 587, secure: 'starttls', connectionTimeout: 10_000, greetingTimeout: 10_000, socketTimeout: 30_000, auth: { username: 'smtp-user', password: 'smtp-password', }, dkim: { domainName: 'example.com', keySelector: 'mail', privateKey: dkimPrivateKey, }, pool: { maxConnections: 2, maxMessages: 100, }, limits: { maxAttachmentSize: 10 * 1024 * 1024, }, }) try { await smtp.verify() const receipt = await sendEmail({ adapter: smtp, from: 'sender@example.com', to: ['recipient@example.com', 'second@example.com'], subject: 'Welcome', envelope: { from: 'bounces@example.com', }, jsx: ( Hello from hono-email. ), attachments: [ { filename: 'invoice.txt', content: 'Invoice text', contentType: 'text/plain', }, { filename: 'logo.png', href: 'https://example.com/assets/logo.png', cid: 'logo', contentDisposition: 'inline', }, ], }) if (!receipt.successful) { console.error(receipt.errorMessages) } } finally { await smtp.close() } ``` For the full list of configuration options, see the [SMTP Options API Reference](/api/adapter-options/#smtp-options). ## Runtime connectors | Entry point | Runtime | | ---------------------------- | ------------------ | | `hono-email/smtp/cloudflare` | Cloudflare Workers | | `hono-email/smtp/node` | Node.js | | `hono-email/smtp/deno` | Deno | | `hono-email/smtp/bun` | Bun | ## Important runtime notes - SMTP transport uses Web Streams internally. Runtime-specific socket support is supplied by the connector. - Cloudflare Workers does not allow outbound SMTP connections on port `25`. Use submission ports such as `465` or `587`. - Bun's TCP API supports direct TLS connections, but the Bun connector does not support STARTTLS upgrade. Use port `465` with `secure: true` on Bun. ## Connection pooling `SmtpTransport` reuses SMTP sessions until `smtp.close()` is called. The default pool size is `1`, so sends on the same transport share one TCP connection sequentially. - Set `pool.maxConnections` to allow multiple concurrent SMTP sessions. - Set `pool.maxMessages` to retire a session after a fixed number of messages. - If a session fails during send, that session is discarded. The message is not retried automatically. ## Delivery controls - `await smtp.verify()` checks connection setup, TLS negotiation, and authentication without sending a message. - `dkim` can be configured on `SmtpTransport` or overridden per message to add a `DKIM-Signature` header before SMTP delivery. - `envelope` lets you override the SMTP envelope sender and recipients without changing the visible `From` / `To` headers. - `to`, `cc`, `bcc`, and `envelope.to` accept single addresses or arrays. SMTP sends one `RCPT TO` command per resolved recipient and reports partial recipient rejection in `receipt.rejected`. ## Options import { Badge } from '@astrojs/starlight/components' ### `connector` **Type:** `SmtpConnector` Runtime-specific TCP socket connector. Import one for your runtime: | Entry point | Runtime | | ---------------------------- | ------------------ | | `hono-email/smtp/node` | Node.js | | `hono-email/smtp/bun` | Bun | | `hono-email/smtp/deno` | Deno | | `hono-email/smtp/cloudflare` | Cloudflare Workers | ### `hostname` **Type:** `string` SMTP server hostname. ### `port` **Type:** `number` SMTP server port. Use `587` for STARTTLS submission, `465` for implicit TLS. ### `secure` **Type:** `boolean | 'starttls'` · **Default:** `'starttls'` TLS mode: | Value | Behavior | | ------------ | ---------------------------------------------- | | `'starttls'` | Upgrade to TLS after connecting (STARTTLS). | | `true` | Implicit TLS from the start of the connection. | | `false` | Plain-text connection with no TLS. | :::caution Bun's TCP connector does not support STARTTLS. Use `secure: true` with port `465` on Bun. ::: ### `auth` **Type:** `{ type?: 'plain' | 'login'; username: string; password: string }` SMTP authentication credentials. `type` defaults to `'plain'`. ### `dkim` **Type:** `EmailDkimOptions` DKIM signing options. See [Email Types](/api/email-types/#emaildkimoptions). ### `clientName` **Type:** `string` Hostname sent in the EHLO/HELO greeting. Defaults to the connector's resolved hostname. ### `connectionTimeout` **Type:** `number` Milliseconds to wait for the TCP connection to be established. ### `greetingTimeout` **Type:** `number` Milliseconds to wait for the server greeting after connecting. ### `socketTimeout` **Type:** `number` Milliseconds of inactivity before the socket is considered timed out. ### `pool` **Type:** `{ maxConnections?: number; maxMessages?: number }` Connection pool settings. - `maxConnections` — maximum concurrent SMTP sessions. Default: `1`. - `maxMessages` — retire a session after this many messages. Default: unlimited. ### `limits.maxAttachmentSize` **Type:** `number` Maximum attachment size in bytes.