Send email from FastAPI with one HTTPS call.

main.py

import os
import httpx
from fastapi import BackgroundTasks, FastAPI
from pydantic import BaseModel, EmailStr

app = FastAPI()

MAILNIX_URL = "https://api.mailnix.ch/v1/messages"
MAILNIX_TOKEN = os.environ["MAILNIX_TOKEN"]  # mnx_live_..., from a secret store


class SignupIn(BaseModel):
    email: EmailStr
    name: str


async def send_welcome_email(to: str, name: str) -> None:
    payload = {
        "from": "hello@yourdomain.com",
        "to": [to],
        "subject": f"Welcome, {name}",
        "html_body": f"<p>Hi {name}, thanks for signing up.</p>",
        "text_body": f"Hi {name}, thanks for signing up.",
        "idempotency_key": f"welcome:{to}",
    }
    headers = {"Authorization": f"Bearer {MAILNIX_TOKEN}"}
    async with httpx.AsyncClient(timeout=10.0) as client:
        resp = await client.post(MAILNIX_URL, json=payload, headers=headers)
        resp.raise_for_status()
        # resp.json() carries the trace_id; log it for your audit trail.


@app.post("/signup", status_code=202)
async def signup(body: SignupIn, background_tasks: BackgroundTasks):
    # Queue the send; the response returns before the email goes out.
    background_tasks.add_task(send_welcome_email, body.email, body.name)
    return {"status": "queued"}

Setup, in order

1. Install httpx and put MAILNIX_TOKEN in your environment or secret store, never in Git.
2. Verify a sending domain in the mailnix dashboard (SPF + DKIM records).
3. Paste the snippet: a Pydantic model, an async send helper with an idempotency_key, and the route.
4. Hit /signup once and look up the returned trace_id in the Traces view.