Compatible API · SMTP2GO

SMTP2GO API compatible: change the URL and the key

SMTP Senpai accepts send requests in the same format as the SMTP2GO API v3 (email). 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 · smtp2go-nodejs 1.0.0 · what changes

  import SMTP2GOApi from 'smtp2go-nodejs';
- const api = SMTP2GOApi(process.env.SMTP2GO_API_KEY);
+ const api = SMTP2GOApi(process.env.SMTP_SENPAI_KEY); // msp_…
  const client = api.client();
+ client.apiUrl = 'https://app.mailsenpai.com/relay/compat/smtp2go/v3/'; // trailing slash

what changes

Two things change, the rest stays

Same paths, same fields, same responses and error shapes as the SMTP2GO API v3 (email).

Base URLhttps://app.mailsenpai.com/relay/compat/smtp2go/v3

Or the dedicated hosthttps://smtp2go-api.mailsenpai.com/v3

Where the key goesX-Smtp2go-Api-Key: msp_… (or api_key in the body)

Paths (unchanged)POST /email/send, /email/mime

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 SMTP2GO format.

the code

Your code, pointed to SMTP Senpai

Node.js · smtp2go-nodejs 1.0.0 · after

import SMTP2GOApi from 'smtp2go-nodejs';
const api = SMTP2GOApi(process.env.SMTP_SENPAI_KEY); // msp_…
const client = api.client();
client.apiUrl = 'https://app.mailsenpai.com/relay/compat/smtp2go/v3/'; // trailing slash

Tested with smtp2go-nodejs 1.0.0: 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 smtp2go-oss/smtp2go-php	subclass ApiClient with API_URL = 'https://smtp2go-api.mailsenpai.com/v3/' and HOST = 'smtp2go-api.mailsenpai.com'	Read in the SDK source code, not yet tested
Python smtp2go	smtp2go.core.API_ROOT = 'https://smtp2go-api.mailsenpai.com/v3/'	Read in the SDK source code, not yet tested

fields

What works, what is ignored, what is refused

Works

sender, to, cc, bcc, subject, html_body, text_body, custom_headers (Reply-To too), attachments, inlines; mime_email

Accepted without effect

—

Named in the X-MailSenpai-Ignored response header.

Refused with the SMTP2GO error

template_id, schedule, attachments by url

The Node SDK needs the trailing slash in apiUrl. The response keeps the SMTP2GO shape: request_id and data with succeeded, failed, failures and email_id.

events and webhooks

Delivery results from the SMTP Senpai API

The SMTP2GO 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 (email_id) 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 SMTP2GO code?

No. You change the base URL (or the host) and the key. Paths, fields, responses and the error format stay those of the SMTP2GO API v3 (email), 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 SMTP2GO 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.

more compatible APIs

The other formats SMTP Senpai accepts

All 14 compatible APIs

The table with every base URL, dedicated host and key.

Open

SendGrid API compatible

SendGrid v3 Mail Send API

Open

Mailgun API compatible

Mailgun Messages API

Open

Amazon SES API compatible

Amazon SES API (v2 SendEmail, v1 SendEmail and SendRawEmail)

Open

Postmark API compatible

Postmark Email API

Open

Resend API compatible

Resend Emails API

Open

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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SMTP2GO is a trademark of Sand Dune Mail Ltd. It is named only to describe the request format SMTP Senpai accepts. MailSenpai is not affiliated with SMTP2GO and this page is not approved by them. Information checked on 9 October 2026.

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