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.

---

SmtpSendOptions

Options passed to smtp.send(message, options).

type SmtpSendOptions = {
  dkim?: EmailDkimOptions
}

dkim Optional

Type: EmailDkimOptions

Signing settings for this send. Takes precedence over legacy message.dkim, then the transport’s dkim default, without merging configurations. Omit to inherit those settings. See DKIM signing for migration from message.dkim.

---

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.

---

AWS SES Options

Options passed to SesAdapter.

SesAdapterOptions

type SesAdapterOptions = {
  client: SesClient
  configurationSetName?: string
  tags?: Readonly<Record<string, string>>
  limits?: EmailAttachmentLimits
}

client Required

Type: SesClient

An AWS SDK v3 SESv2Client. Configure region, credentials, timeouts, and retries on this client. The adapter reuses the client without destroying it.

configurationSetName Optional

Type: string

Default SES configuration set.

tags Optional

Type: Readonly<Record<string, string>>

Default SES event tags.

limits Optional

Type: EmailAttachmentLimits

Attachment limits.

SesSendOptions

Options passed to adapter.send(message, options) for individual sends. The shared sendEmail() helper uses the adapter defaults.

type SesSendOptions = {
  configurationSetName?: string
  tags?: Readonly<Record<string, string>>
  abortSignal?: AbortSignal
}

configurationSetName Optional

Type: string

Overrides the default configuration set for this send.

tags Optional

Type: Readonly<Record<string, string>>

Merged with the default tags by key, with per-send values taking precedence.

abortSignal Optional

Type: AbortSignal

Cancellation signal forwarded to the SDK request. Does not cancel rendering or attachment loading.

---

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
}