Microsoft 365 Tenant Checker

Small Flask-based utility that queries Microsoft's Autodiscover endpoint to determine if a domain is tied to a Microsoft 365 tenant (Exchange Online, Teams, etc.). It exposes a JSON API and a lightweight HTML page, ready for Docker or Render.com deployment.

Demo and repository

• Live demo: https://m365-tenant-checker.onrender.com
• Source code: github.com/gioxx/m365-tenant-checker

Key features

• 🔎 Instant domain check against Autodiscover. -, REST API: GET /check?domain=example.com returning JSON.
• 🌐 Minimal web interface with Light/Dark toggle.
• 🐳 Public Docker image (ghcr.io/gioxx/m365-tenant-checker:latest).
• ☁️ Render.com-ready via gunicorn.

Architecture at a glance

• Backend (backend/app.py): Flask serves /check and the static page. It issues a GET to https://autodiscover-s.outlook.com/autodiscover/autodiscover.json?Email=test@<domain>&Protocol=Autodiscoverv1 with a 5s timeout.
• Frontend (frontend/index.html): Single input form, fetches /check, shows textual feedback, includes a theme toggle.
• Container (Dockerfile): Python slim image, installs Flask, requests, flask-cors, gunicorn; exposes :5000 and starts gunicorn backend.app:app.
• Procfile: web: gunicorn backend.app:app for Render.com.

API

• Endpoint: GET /check?domain=<domain>
• Parameter: domain (required). Missing parameter → 400 Bad Request.
• Typical responses

HTTP	found	message
200	true	Domain associated with M365; redirect URL returned when available.
200	true	Domain replied 200 but without URL / invalid JSON.
404	false	Domain is not associated with Microsoft 365.
400	null	Protocol error (missing Protocol=Autodiscoverv1) or malformed request.
500	null	Internal error / timeout toward Autodiscover.

Example

curl "http://localhost:5000/check?domain=contoso.com"

{
  "domain": "contoso.com",
  "status": 200,
  "found": true,
  "message": "Domain is associated with Microsoft 365. Redirect URL: https://outlook.office365.com/autodiscover/autodiscover.xml"
}

Quick start

Docker (recommended)

docker pull ghcr.io/gioxx/m365-tenant-checker:latest
docker run -p 5000:5000 ghcr.io/gioxx/m365-tenant-checker:latest

Open http://localhost:5000 for the UI, or call /check.

Docker Compose (single service)

compose.yaml

services:
  m365-tenant-checker:
    image: ghcr.io/gioxx/m365-tenant-checker:latest
    ports:
      - "5000:5000"
    restart: unless-stopped

Run it:

docker compose up -d

Browse http://localhost:5000.

Local run (no Docker)

python -m venv .venv
source .venv/bin/activate  # on Windows: .venv\Scripts\activate
pip install -r backend/requirements.txt
gunicorn backend.app:app --bind 0.0.0.0:5000
# dev alternative: flask --app backend.app run --host 0.0.0.0 --port 5000

Render.com

1. Create a Web Service.
2. Connect the GitHub repo.
3. Set: Build Command empty; Start Command gunicorn backend.app:app; Runtime Python 3; Instance Type Free.
4. Deploy.

Repository structure

m365-tenant-checker/
├── backend/
│   ├── app.py              # /check endpoint and static serving
│   └── requirements.txt
├── frontend/
│   └── index.html          # Minimal UI with theme toggle
├── Dockerfile              # Image published to ghcr.io
├── Procfile                # Render.com startup
├── README.md / README-IT.md
└── LICENSE

Operational notes

• No authentication or rate limiting: place behind a reverse proxy if exposed publicly.
• Backend uses requests with a 5s timeout; network issues return 500.
• HTML is served directly by Flask (/), so no separate static server is required.
• Dockerfile currently uses Python 3.15 slim; pin to an LTS version if needed for production.