Mailjet API compatible: change the URL and the key
SMTP Senpai accepts send requests in the same format as the Mailjet Send API v3.1. 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
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const Mailjet = require('node-mailjet'); - const mailjet = Mailjet.apiConnect(process.env.MJ_APIKEY_PUBLIC, process.env.MJ_APIKEY_PRIVATE); + const key = process.env.SMTP_SENPAI_KEY; // msp_… + const mailjet = Mailjet.apiConnect(key, key, { + config: { host: 'app.mailsenpai.com/relay/compat/mailjet' }, + }); + // then, as before: mailjet.post('send', { version: 'v3.1' }).request({ Messages: [...] })
Two things change, the rest stays
Same paths, same fields, same responses and error shapes as the Mailjet Send API v3.1.
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 Mailjet format. To try without sending, use SandboxMode: the request is checked and nothing leaves.
Your code, pointed to SMTP Senpai
const Mailjet = require('node-mailjet');
const key = process.env.SMTP_SENPAI_KEY; // msp_…
const mailjet = Mailjet.apiConnect(key, key, {
config: { host: 'app.mailsenpai.com/relay/compat/mailjet' },
});
// then, as before: mailjet.post('send', { version: 'v3.1' }).request({ Messages: [...] })Tested with node-mailjet 6.0.11: run with the official SDK against the SMTP Senpai endpoints.
Other languages and frameworks
Settings read in the source code of each SDK: they follow the same rule (base URL or host, plus your key). Try them with a test send before going live.
| SDK | Setting | Status |
|---|---|---|
| PHP mailjet/mailjet-apiv3-php | new \Mailjet\Client($key, $key, true, ['version' => 'v3.1', 'url' => 'app.mailsenpai.com/relay/compat/mailjet']) | Read in the SDK source code, not yet tested |
| Go mailjet-apiv3-go | mailjet.NewMailjetClient(key, key, "https://app.mailsenpai.com/relay/compat/mailjet/v3") | Read in the SDK source code, not yet tested |
What works, what is ignored, what is refused
Works
Messages (up to 50) with From, To, Cc, Bcc, ReplyTo, Subject, TextPart, HTMLPart, Headers, Attachments, InlinedAttachments, Variables with TemplateLanguage ({{var:name}}), Globals, SandboxMode
Accepted without effect
CustomID, EventPayload, CustomCampaign, DeduplicateCampaign, URLTags, Priority, TrackOpens, TrackClicks
Named in the X-MailSenpai-Ignored response header.
Refused with the Mailjet error
TemplateID
The Python SDK mailjet_rest (1.6 and later) only accepts *.mailjet.com hosts, so it cannot be pointed elsewhere: call the HTTP API directly (Basic auth with the key as user and password). Each message gets its own result.
Delivery results from the SMTP Senpai API
The Mailjet 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 (MessageUUID) 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 Mailjet code?
No. You change the base URL (or the host) and the key. Paths, fields, responses and the error format stay those of the Mailjet Send API v3.1, 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 Mailjet event and webhook endpoints are not reproduced.
Can I test without sending?
Yes, as with Mailjet: set SandboxMode. The request is checked and nothing is sent.
Does the Python SDK work?
Not the official one from version 1.6: it only accepts *.mailjet.com hosts. Call the HTTP API directly, with the key as both user and password.
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.
Mailjet is a trademark of Mailjet SAS, a Sinch group company. It is named only to describe the request format SMTP Senpai accepts. MailSenpai is not affiliated with Mailjet or Sinch and this page is not approved by them. Information checked on 9 October 2026.