send_email

Send an email via the Resend API or SMTP.

Parameters

Common Parameters

Resend-specific Parameters

Parameter	Type	Required	Default	Description
api_key	string	no	env RESEND_API_KEY	Resend API key.
api_url	string	no	"https://api.resend.com/emails"	Explicit Resend-compatible endpoint, including a local test fixture.

SMTP-specific Parameters

Parameter	Type	Required	Default	Description
smtp_server	string	no	env SMTP_SERVER	SMTP server hostname.
smtp_port	number	no	env SMTP_PORT or provider default	SMTP port (587 for STARTTLS, 465 for TLS, 25 for none).
smtp_username	string	no	env SMTP_USERNAME	SMTP authentication username.
smtp_password	string	no	env SMTP_PASSWORD	SMTP authentication password.
smtp_tls	string	no	"starttls"	TLS mode: "starttls" (default), "tls" (implicit), or "none".

HTTP Transport

Resend API requests follow redirects only within the original scheme, host, and effective port, with at most 10 hops. Cross-origin redirects fail before replaying email content; automatic Referer is disabled. Configure the final API endpoint explicitly when its origin changes. This policy does not change the SMTP provider.

Resend success and error response bodies share IRONFLOW_MAX_HTTP_BODY_BYTES (default 52428800, 50 MiB). An oversized Content-Length fails before body collection; actual bytes are checked before each chunk is retained, including chunked responses. Exceeding the cap, an interrupted body, timeout, or run cancellation fails or cancels the step without publishing partial email output. The limit counts received body bytes before charset/BOM decoding. It is not a total-memory or decoded-JSON limit. The SMTP provider is unaffected.

Within-limit non-2xx responses still fail with their status and redacted body detail. Oversized responses fail with the size error before provider body parsing. A failed response read does not prove the email was not delivered; retrying can send the email again.

Context Output

• {output_key}_status — HTTP status code (Resend) or SMTP response code.
• {output_key}_data — Response body (Resend JSON if parseable, otherwise decoded text) or SMTP response details.
• {output_key}_success — true on success.

Environment Variables

Variable	Description
RESEND_API_KEY	Resend API key (fallback when api_key is not in config)
SENDER_EMAIL	Default sender address (fallback when from is not in config)
SMTP_SERVER	SMTP server hostname
SMTP_PORT	SMTP server port
SMTP_USERNAME	SMTP authentication username
SMTP_PASSWORD	SMTP authentication password

Examples

Resend API

The runnable Resend example reads the optional RESEND_API_URL environment variable into api_url for a local HTTP fixture; omitting it retains the normal API endpoint. This variable is an example convention, not a node-level fallback. Keep API credentials synthetic when testing against an alternate endpoint.

local flow = Flow.new("send_email_resend")

flow:step("send", nodes.send_email({
    to = env("SENDER_EMAIL"),
    subject = "Welcome to IronFlow!",
    html = "<h1>Welcome!</h1><p>Your workflow engine is ready.</p>",
    text = "Welcome! Your workflow engine is ready."
}))

flow:step("log", nodes.log({
    message = "Email result: success=${ctx.email_success}, data=${ctx.email_data}"
})):depends_on("send")

return flow

SMTP

local flow = Flow.new("send_email_smtp")

flow:step("send", nodes.send_email({
    provider = "smtp",
    to = env("SENDER_EMAIL"),
    subject = "IronFlow SMTP Test",
    html = "<h1>Hello!</h1><p>Sent via SMTP.</p>",
    text = "Hello! Sent via SMTP."
}))

return flow

Multiple recipients

flow:step("notify_team", nodes.send_email({
    to = { "[email protected]", "[email protected]" },
    from = "[email protected]",
    subject = "Deploy complete: ${ctx.version}",
    html = "<p>Version <b>${ctx.version}</b> deployed.</p>",
    cc = "[email protected]",
    output_key = "deploy_email"
}))