Plunk API compatible: change the URL and the key
SMTP Senpai accepts send requests in the same format as the Plunk send API. Point your code to SMTP Senpai, use your msp_ key and keep your SDK, your fields and your error handling.
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- Same paths, fields and errors
- Sending servers and log in the EU
- 14-day free trial
import Plunk from '@plunk/node'; - const plunk = new Plunk(process.env.PLUNK_API_KEY); + const plunk = new Plunk(process.env.SMTP_SENPAI_KEY, { // msp_… + baseUrl: 'https://app.mailsenpai.com/relay/compat/plunk/v1/', // trailing slash + });
Two things change, the rest stays
Same paths, same fields, same responses and error shapes as the Plunk send API.
The sender must be on a domain verified in your SMTP Senpai area and signed with DKIM: otherwise the request is refused with an error in the Plunk format.
Your code, pointed to SMTP Senpai
import Plunk from '@plunk/node';
const plunk = new Plunk(process.env.SMTP_SENPAI_KEY, { // msp_…
baseUrl: 'https://app.mailsenpai.com/relay/compat/plunk/v1/', // trailing slash
});Tested with @plunk/node 3.0.3: run with the official SDK against the SMTP Senpai endpoints.
What works, what is ignored, what is refused
Works
to (one email per recipient), subject, body (HTML), from, reply, headers, attachments, data ({{name}}), Idempotency-Key
Accepted without effect
—
Named in the X-MailSenpai-Ignored response header.
Refused with the Plunk error
template
Only the send endpoint is covered: Plunk contacts, events and automations are not part of SMTP Senpai. The baseUrl needs the trailing slash.
Delivery results from the SMTP Senpai API
The Plunk endpoints for logs, events, statistics and webhooks are not reproduced. Results (sent, delivered, bounce, defer, complaint, dropped, open, click) come from the SMTP Senpai API with the same key: GET /relay/v1/eventi, or a signed webhook set in your SMTP Senpai area.
The id in the send response is the message_id of those events. Each response also carries X-MailSenpai-Result (sent, queued, suppressed, failed).
Read the events and webhook reference
curl "https://app.mailsenpai.com/relay/v1/eventi?quanti=50" \
-H "Authorization: Bearer $SMTP_SENPAI_KEY"
# {"ok": true, "eventi": [{"type": "delivered",
# "email": "…", "message_id": "…", …}], "prossimo": …}Frequently asked questions
Do I have to rewrite my Plunk code?
No. You change the base URL (or the host) and the key. Paths, fields, responses and the error format stay those of the Plunk send API, so your SDK and your error handling keep working.
What about templates and scheduled sending?
They are not supported: requests that use them are refused with the native error, so nothing leaves by mistake. Build the final content in your code and send it when you want it to leave.
How do I get bounces, opens and webhooks?
From the SMTP Senpai API, with the same key: GET /relay/v1/eventi or a signed webhook set in your SMTP Senpai area. The Plunk event and webhook endpoints are not reproduced.
Can I keep sending through SMTP?
Yes. The same account also works over SMTP (relay.mailsenpai.com, port 2525, STARTTLS) and with the SMTP Senpai REST API.
The other formats SMTP Senpai accepts
All 14 compatible APIs
The table with every base URL, dedicated host and key.
OpenSendGrid API compatible
SendGrid v3 Mail Send API
OpenMailgun API compatible
Mailgun Messages API
OpenAmazon SES API compatible
Amazon SES API (v2 SendEmail, v1 SendEmail and SendRawEmail)
OpenPostmark API compatible
Postmark Email API
OpenResend API compatible
Resend Emails API
OpenTry SMTP Senpai with your current code
14 days to change the base URL and the key, send your real emails and check every result in the log. Then decide.
Plunk is an open-source project (useplunk) and a trademark of its owner. It is named only to describe the request format SMTP Senpai accepts. MailSenpai is not affiliated with the Plunk project and this page is not approved by them. Information checked on 9 October 2026.