Adapter Options

Each delivery adapter has specific configuration options passed when initializing the transport or adapter function.

---

SMTP Options

SMTP settings used with SmtpTransport.

SmtpTransportOptions

type SmtpTransportOptions = {
  connector: SmtpConnector
  hostname: string
  port: number
  secure?: boolean | 'starttls'
  auth?: SmtpAuth
  dkim?: EmailDkimOptions
  clientName?: string
  connectionTimeout?: number
  greetingTimeout?: number
  socketTimeout?: number
  limits?: EmailAttachmentLimits
  pool?: {
    maxConnections?: number
    maxMessages?: number
  }
}

connector Required

Type: SmtpConnector

Runtime-specific socket connector. Built-in connectors are available for different runtimes (e.g. nodeSmtpConnector for Node.js, cloudflareSmtpConnector for Cloudflare Workers).

hostname Required

Type: string

SMTP server host name (e.g., 'smtp.gmail.com').

port Required

Type: number

SMTP server port (e.g., 587 or 465).

secure Optional

Type: boolean | 'starttls'

TLS mode. true uses implicit TLS (usually on port 465), 'starttls' upgrades the connection using STARTTLS after the initial handshake (usually on port 587).

auth Optional

Type: SmtpAuth

Authentication configuration. See SmtpAuth.

dkim Optional

Type: EmailDkimOptions

Default DKIM signing options for all outgoing messages on this transport. See EmailDkimOptions.

clientName Optional

Type: string · Default: 'localhost'

Name sent during the SMTP EHLO/HELO handshake.

connectionTimeout Optional

Type: number

Connection timeout in milliseconds.

greetingTimeout Optional

Type: number

Greeting timeout in milliseconds.

socketTimeout Optional

Type: number

Socket idle timeout in milliseconds.

limits Optional

Type: EmailAttachmentLimits

Attachment size limits.

pool Optional

• maxConnections: Maximum number of concurrent connections in the pool (Default: 1).
• maxMessages: Maximum number of messages to send over a single connection before retiring it.

---

SmtpAuth

type SmtpAuth =
  | {
      type?: 'plain'
      username: string
      password: string
    }
  | {
      type: 'login'
      username: string
      password: string
    }

• type: Mechanism used for SMTP authentication ('plain' or 'login').
• username: Username credential.
• password: Password credential.

---

SMTP Connector Interfaces

When using SmtpTransport, the runtime-specific socket creation is handled by a connector.

SmtpConnector

type SmtpConnector = {
  connect(
    address: SmtpSocketAddress,
    options: SmtpConnectorOptions,
  ): SmtpSocket | Promise<SmtpSocket>
}

• SmtpSocketAddress: An object containing { hostname: string, port: number }.
• SmtpConnectorOptions: Contains { secureTransport: 'off' | 'on' | 'starttls' }.

SmtpSocket

An abstraction layer for the underlying TCP connection:

type SmtpSocket = {
  readable: ReadableStream<Uint8Array>
  writable: WritableStream<Uint8Array>
  opened?: Promise<unknown>
  closed?: Promise<void>
  startTls?: () => SmtpSocket | Promise<SmtpSocket>
  close?: () => Promise<void> | void
}

---

Resend Options

Options passed to ResendAdapter.

ResendAdapterOptions

type ResendAdapterOptions = {
  apiKey: string
  apiBaseUrl?: string
  fetch?: ResendFetch
  limits?: EmailAttachmentLimits
  userAgent?: string
}

apiKey Required

Type: string

Resend API Key.

apiBaseUrl Optional

Type: string · Default: 'https://api.resend.com'

Custom API base URL override.

fetch Optional

Type: ResendFetch

Custom fetch implementation. If omitted, uses the global fetch of the current environment.

limits Optional

Type: EmailAttachmentLimits

Attachment limits.

---

SendGrid Options

Options passed to SendGridAdapter.

SendGridAdapterOptions

type SendGridAdapterOptions = {
  apiKey: string
  apiBaseUrl?: string
  fetch?: SendGridFetch
  limits?: EmailAttachmentLimits
  userAgent?: string
}

apiKey Required

Type: string

SendGrid API Key (Bearer Token).

apiBaseUrl Optional

Type: string · Default: 'https://api.sendgrid.com'

Custom API base URL override.

---

Postmark Options

Options passed to PostmarkAdapter.

PostmarkAdapterOptions

type PostmarkAdapterOptions = {
  serverToken: string
  apiBaseUrl?: string
  fetch?: PostmarkFetch
  limits?: EmailAttachmentLimits
  messageStream?: string
  tag?: string
  trackLinks?: 'HtmlAndText' | 'HtmlOnly' | 'None' | 'TextOnly'
  trackOpens?: boolean
  userAgent?: string
}

serverToken Required

Type: string

Postmark Server Token.

messageStream Optional

Type: string

Specifies the Postmark Message Stream ID to send through (e.g., 'outbound').

tag Optional

Type: string

Default category/tag for emails sent via this adapter.

trackLinks / trackOpens Optional

Enable link tracking or open tracking behavior at the adapter level.

---

Mailgun Options

Options passed to MailgunAdapter.

MailgunAdapterOptions

type MailgunAdapterOptions = {
  apiKey: string
  domain: string
  apiBaseUrl?: string
  fetch?: MailgunFetch
  limits?: EmailAttachmentLimits
  userAgent?: string
}

apiKey Required

Type: string

Mailgun API key.

domain Required

Type: string

Mailgun verified sending domain (e.g., 'mg.example.com').

apiBaseUrl Optional

Type: string · Default: 'https://api.mailgun.net'

For EU region domains, set this to 'https://api.eu.mailgun.net'.

---

Cloudflare Email Options

Options passed to CloudflareEmailAdapter.

CloudflareEmailAdapterOptions

type CloudflareEmailAdapterOptions = {
  connector: CloudflareEmailConnector
  limits?: EmailAttachmentLimits
}

connector Required

Type: CloudflareEmailConnector

Connector targeting the specific Cloudflare infrastructure.

• RESTConnector({ accountId, apiToken }): Calls the Cloudflare Email REST API.
• WorkersConnector({ bindingName }): Sends through a native Cloudflare Workers Email Routing binding (default binding name is 'EMAIL').

---

Cloudflare Email Connector Interfaces

CloudflareEmailAdapter requires a connector implementing the CloudflareEmailConnector interface.

CloudflareEmailConnector

type CloudflareEmailConnector = {
  send(
    request: CloudflareEmailConnectorRequest,
  ): CloudflareEmailConnectorResult | Promise<CloudflareEmailConnectorResult>
}

CloudflareEmailRestConnectorOptions

Options for configuring the RESTConnector:

type CloudflareEmailRestConnectorOptions = {
  accountId: string
  apiBaseUrl?: string
  apiToken: string
  fetch?: CloudflareEmailFetch
}

CloudflareEmailWorkersConnectorOptions

Options for configuring the WorkersConnector:

type CloudflareEmailWorkersConnectorOptions = {
  bindingName?: string
}