Send email in n8n over SMTP or the REST API

n8n can send through Postwing two ways. The Send Email node speaks SMTP and needs nothing but a credential. The HTTP Request node calls the REST API instead, which adds saved templates, safe retries and a message id to track. Both authenticate with the same domain token.

SMTP connection settings

Create the SMTP credential

Add a Send Email node, open Credential to connect with and create a new SMTP credential:

Configure the Send Email node

The From address is what DKIM, SPF and DMARC are checked against. Put a customer's address there — say, from a form submission — and the message is refused; use Reply To for it instead.

Send a test email

Put your own address in To Email and execute the node on its own. A failure shows the SMTP server's reply in the node's output, which tells you whether the port, the encryption or the credentials are wrong.

Or: the HTTP Request node

Configure an HTTP Request node with Method POST, URLhttps://api.postwing.app/external/send_email_simple/, Authentication None, Send Body on, Body Content Type JSON and Specify Body Using JSON. Switch the JSON field to an expression and paste:

{
  "to": [{{ JSON.stringify($json.email) }}],
  "subject": {{ JSON.stringify($json.subject) }},
  "body": {{ JSON.stringify($json.html) }},
  "sender": "Acme <noreply@your-domain.com>",
  "idempotency_key": {{ JSON.stringify("order-" + $json.orderId) }},
  "auth": {
    "username": "token-login@your-domain.com",
    "password": "your-token-password"
  }
}

JSON.stringify quotes and escapes each value, so HTML full of quotes and line breaks cannot break the body. The token travels in the body because that is how the send API authenticates — n8n's credential store has no slot for it here, so anyone who can edit or export the workflow can read it. The idempotency_key makes a repeated request return the first result instead of sending again. The rest of the fields are in the API reference.

The node also has Import cURL. Pasting this fills in the method, URL, header and body in one go:

curl -X POST https://api.postwing.app/external/send_email_simple/ \
  -H "Content-Type: application/json" \
  -d '{"to": ["you@your-domain.com"], "subject": "Test", "body": "<p>It works.</p>",
       "sender": "Acme <noreply@your-domain.com>",
       "auth": {"username": "token-login@your-domain.com", "password": "your-token-password"}}'

Troubleshooting