Compatible API · Elastic Email

Elastic Email API compatible: change the URL and the key

SMTP Senpai accepts send requests in the same format as the Elastic Email API v4 (emails). 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
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Node.js · @elasticemail/elasticemail-client 4.2.1 · what changes

  const ElasticEmail = require('@elasticemail/elasticemail-client');
  const client = ElasticEmail.ApiClient.instance;
+ client.basePath = 'https://app.mailsenpai.com/relay/compat/elasticemail/v4';
- client.authentications['apikey'].apiKey = process.env.ELASTIC_EMAIL_API_KEY;
+ client.authentications['apikey'].apiKey = process.env.SMTP_SENPAI_KEY; // msp_…

what changes

Two things change, the rest stays

Same paths, same fields, same responses and error shapes as the Elastic Email API v4 (emails).

Base URLhttps://app.mailsenpai.com/relay/compat/elasticemail/v4

Or the dedicated hosthttps://elasticemail-api.mailsenpai.com/v4

Where the key goesX-ElasticEmail-ApiKey: msp_…

Paths (unchanged)POST /emails/transactional, /emails

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 Elastic Email format.

the code

Your code, pointed to SMTP Senpai

Node.js · @elasticemail/elasticemail-client 4.2.1 · after

const ElasticEmail = require('@elasticemail/elasticemail-client');
const client = ElasticEmail.ApiClient.instance;
client.basePath = 'https://app.mailsenpai.com/relay/compat/elasticemail/v4';
client.authentications['apikey'].apiKey = process.env.SMTP_SENPAI_KEY; // msp_…

Tested with @elasticemail/elasticemail-client 4.2.1: 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 elasticemail/elasticemail-php	Configuration::getDefaultConfiguration()->setHost('https://app.mailsenpai.com/relay/compat/elasticemail/v4')->setApiKey('X-ElasticEmail-ApiKey', $key)	Read in the SDK source code, not yet tested
Python ElasticEmail	Configuration(host='https://app.mailsenpai.com/relay/compat/elasticemail/v4')	Read in the SDK source code, not yet tested

fields

What works, what is ignored, what is refused

Works

Recipients (To/CC/BCC, or a list with Fields for one email per recipient), Content.Body (HTML, PlainText), From, ReplyTo, Subject, Headers, Attachments (BinaryContent), Merge ({field})

Accepted without effect

Options.TrackOpens, TrackClicks, PoolName, ChannelName, Postback, Utm

Named in the X-MailSenpai-Ignored response header.

Refused with the Elastic Email error

TemplateName, Options.TimeOffset

Only the email send endpoints of API v4 are covered: contacts, lists, campaigns and the older v2 API are not.

events and webhooks

Delivery results from the SMTP Senpai API

The Elastic Email 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

Limits. Up to 50 recipients per message and 500 copies per request (over 50 they are queued and leave within about a minute), 10 attachments and 10 MB per message. Templates and scheduled sending are not supported: send the final content when you want it to leave.

Terminal · SMTP Senpai events

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 Elastic Email code?

No. You change the base URL (or the host) and the key. Paths, fields, responses and the error format stay those of the Elastic Email API v4 (emails), 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 Elastic Email 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.

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Try 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.

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Elastic Email is a trademark of Elastic Email Inc.. It is named only to describe the request format SMTP Senpai accepts. MailSenpai is not affiliated with Elastic Email and this page is not approved by them. Information checked on 9 October 2026.

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