Mail API · by WebXIO
SMTP-Relay takes your application's mail through a REST API, fills in the template in the right language and delivers it through your own mail account: Microsoft 365, Google or any SMTP server. With a queue, retries and a log, operated by WebXIO in Europe.
Request
curl -X POST https://admin.smtp.webxio.at/api/v1/send \
-H "Authorization: Bearer $SMTP_RELAY_KEY" \
-H "Content-Type: application/json" \
-d '{
"to": "anna@example.com",
"templateId": 7,
"language": "de-AT",
"variables": { "firstName": "Anna" }
}'Response
HTTP/1.1 202 Accepted
X-RateLimit-Limit: 60
X-RateLimit-Remaining: 59
{ "id": 42, "status": "queued", "language": "de" }01How it works
Your application sends one request, the relay does the rest: check, render, queue, deliver.
Sends recipients, template and variables as JSON, authenticated with its project's API key.
Bearer srk_…Key, rate limit and content are checked. As soon as the mail is queued, the API answers with an ID.
202 AcceptedThe template is rendered in the matching language: the exact one, then the base language, then English, then German.
HandlebarsUp to 5 attempts with growing pauses. Permanent errors such as an unknown recipient are not retried.
BullMQ · ValkeyMail goes out through your project's SMTP account: Microsoft 365, Google or any other server, over SSL, TLS or STARTTLS if you like.
SMTPThe status changes to “sent”, with message ID and timestamp. Available through the API and in the log.
status: sentMail is sent through your own account: sender address, SPF and DKIM stay with your mail provider.
02Features
What your application would otherwise have to build itself is part of the relay, managed in the admin UI.
Subject, HTML and text with placeholders, conditions and loops. In the admin UI with a visual editor and live preview.
Up to 50 translations per template. You send the language along, the relay picks the matching translation.
Every mail goes into the queue first. If sending fails, the relay tries up to 5 times.
Several SMTP accounts per project, one of them the default. Pick another one per mail with accountId.
Every project gets its own named keys, for production and testing for example. Revoking takes one click.
Every mail with status, attempts and last error, filterable by project, status and free text.
Not available yet, but on the way:
03API
A POST with JSON is all it takes, from any language and any framework. Look up the status of every mail by its ID.
templateId, variables and optionally language. Content and translations live in the admin UI, your code stays lean.
subject plus html and/or text right in the request, for mail whose content your application generates itself.
Use the API key on the server only, never in the browser.
curl …/api/v1/messages/42 Look up the status
{
"id": 42,
"status": "sent",
"attempts": 2,
"language": "de",
"messageId": "<5f1c…@example.com>",
"sentAt": "2026-09-29T09:14:03.000Z",
"error": null
}04Operations
The relay is built to be traceable: every accepted mail has an ID, a status and a history.
The API only answers once the mail is safely in the queue. Otherwise you get a 503, and your application knows.
SMTP passwords are stored AES-256-GCM encrypted, API keys only as a SHA-256 hash.
Every user only sees their own mail accounts, templates and projects.
Mail goes out through your own account. Sender address, reputation, SPF and DKIM stay with your provider.
Operated by WebXIO on its own infrastructure in Europe, built and shipped through its own GitLab.
The relay sends its own sign-in mails through itself, as well as the contact forms of webxio.at and this site.
A lean stack of proven, open building blocks.
05FAQ
Straight answers to the most common questions.
No. There is no port for mail clients to connect to. Your application talks to an HTTPS API, and the relay then sends through an SMTP account.
Yes, mail is sent through an SMTP account, such as Microsoft 365, Google Workspace or your host's. If you don't have one yet, choose “advice wanted” in the form.
Not yet. Those records belong to your domain and your mail provider, which signs the mail. DKIM support in the relay is planned.
Not yet. All three are planned, as are open and click tracking. Until then, look up the delivery status with GET /api/v1/messages/:id.
It's not needed: one HTTP request does it, from any language. The admin UI shows a ready-made curl call for every project.
60 mails per minute per project by default, at most 100. Your mail provider's limits apply too: Microsoft 365, for example, allows 30 per minute.
No. Without unsubscribe links and bounce handling, the relay is meant for transactional mail: confirmations, notifications, contact forms.
Through the form below. Accounts are created by a person, there is no self sign-up. Then you set up your mail account, templates and project in the admin UI, together with us if you like.
06Access
Accounts are set up by a person, not a machine. Tell us briefly what you need the relay for.