Mailgun API compatible: change the URL and the key
SMTP Senpai accepts send requests in the same format as the Mailgun Messages 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
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import Mailgun from 'mailgun.js'; import FormData from 'form-data'; const mailgun = new Mailgun(FormData); - const mg = mailgun.client({ username: 'api', key: process.env.MAILGUN_API_KEY }); + const mg = mailgun.client({ + username: 'api', + key: process.env.SMTP_SENPAI_KEY, // msp_… + url: 'https://app.mailsenpai.com/relay/compat/mailgun', + });
Two things change, the rest stays
Same paths, same fields, same responses and error shapes as the Mailgun Messages 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 Mailgun format. To try without sending, use o:testmode=yes: the request is checked and nothing leaves.
Your code, pointed to SMTP Senpai
import Mailgun from 'mailgun.js';
import FormData from 'form-data';
const mailgun = new Mailgun(FormData);
const mg = mailgun.client({
username: 'api',
key: process.env.SMTP_SENPAI_KEY, // msp_…
url: 'https://app.mailsenpai.com/relay/compat/mailgun',
});Tested with mailgun.js 14.1.0: 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 mailgun/mailgun-php | Mailgun::create($key, 'https://mailgun-api.mailsenpai.com') | Read in the SDK source code, not yet tested |
| Ruby mailgun-ruby | Mailgun::Client.new(key, 'app.mailsenpai.com/relay/compat/mailgun') | Read in the SDK source code, not yet tested |
| Python mailgun | Client(auth=('api', key), api_url='https://app.mailsenpai.com/relay/compat/mailgun') | Read in the SDK source code, not yet tested |
| Laravel | 'mailgun' => ['domain' => 'yourdomain.com', 'secret' => KEY, 'endpoint' => 'mailgun-api.mailsenpai.com', 'scheme' => 'https'] | Read in the SDK source code, not yet tested |
| Symfony Mailer | MAILER_DSN=mailgun+api://KEY:[email protected] | Read in the SDK source code, not yet tested |
What works, what is ignored, what is refused
Works
from, to (repeated or comma-separated), cc, bcc, subject, text, html, attachment, inline (cid:), h:
Accepted without effect
o:tag, o:tracking*, other o: options, v: variables, amp-html
Named in the X-MailSenpai-Ignored response header.
Refused with the Mailgun error
template, t: options, o:deliverytime and the other scheduling options (400)
The domain in the path must be one of your sending domains verified in SMTP Senpai. Multipart and urlencoded bodies both work; repeated to fields and several attachments are kept.
Delivery results from the SMTP Senpai API
The Mailgun 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 Mailgun code?
No. You change the base URL (or the host) and the key. Paths, fields, responses and the error format stay those of the Mailgun Messages 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 Mailgun event and webhook endpoints are not reproduced.
Can I test without sending?
Yes, as with Mailgun: set o:testmode=yes. The request is checked and nothing is sent.
Which domain goes in the path?
One of your sending domains verified in SMTP Senpai, as /v3/yourdomain.com/messages.
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
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
OpenBrevo API compatible
Brevo transactional email 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.
Mailgun is a trademark of Mailgun Technologies, Inc., a Sinch group company. It is named only to describe the request format SMTP Senpai accepts. MailSenpai is not affiliated with Mailgun or Sinch and this page is not approved by them. Information checked on 9 October 2026.