autodiscover-worker

Cloudflare Worker that reverse-proxies Exchange Autodiscover requests to a configurable upstream endpoint.

Problem

When using hosted Exchange-compatible mail services (e.g. AWS WorkMail), email clients like Outlook perform Autodiscover to automatically configure mailbox settings. The process has three phases:

• Phase 1 — SCP lookup in Active Directory (domain-joined clients only)
• Phase 2 — HTTPS POST to https://<domain>/autodiscover/autodiscover.xml and https://autodiscover.<domain>/autodiscover/autodiscover.xml
• Phase 3 — Unauthenticated HTTP GET to http://autodiscover.<domain>/autodiscover/autodiscover.xml, following 302 redirects

A common approach is to set a CNAME record pointing autodiscover.<domain> to the mail service. However, this only enables Phase 3 (HTTP redirect). Some email clients on Android and iOS — such as the built-in mail apps — do not support Phase 3 and rely solely on Phase 2 (direct HTTPS). For these clients, the CNAME approach results in Autodiscover failure on mobile devices.

This worker solves the problem by sitting at autodiscover.<domain> on Cloudflare and directly proxying HTTPS requests to your upstream Autodiscover endpoint, enabling both Phase 2 and Phase 3 to work across all clients.

How It Works

Email Client                  Cloudflare Worker                    Mail Service
    |                               |                                   |
    |  POST /autodiscover/...       |                                   |
    |------------------------------>|                                   |
    |  (autodiscover.example.com)   |  Rewrite host → upstream          |
    |                               |---------------------------------->|
    |                               |          Autodiscover response    |
    |          Response             |<----------------------------------|
    |<------------------------------|                                   |

The worker rewrites the request hostname to the configured UPSTREAM value and proxies the request as-is, preserving method, headers, and body.

Configuration

Environment Variable	Description	Example
UPSTREAM	Autodiscover endpoint hostname of your mail service	autodiscover-service.mail.us-west-2.awsapps.com

See wrangler.jsonc.example for a full configuration reference.

Deployment

Prerequisites

• A Cloudflare account with your domain configured
• Node.js 24+, pnpm

1. Fork and Clone

Fork this repository to your own GitHub account, then clone it:

git clone https://github.com/<your-username>/autodiscover-worker.git
cd autodiscover-worker
pnpm install

2. Configure

You can configure the worker in two ways:

Option A: Via wrangler.jsonc

Edit wrangler.jsonc to add your environment variable and custom domain:

{
  "$schema": "node_modules/wrangler/config-schema.json",
  "name": "autodiscover-worker",
  "main": "src/index.ts",
  "compatibility_date": "2025-04-01",
  "vars": {
    "UPSTREAM": "autodiscover-service.mail.us-west-2.awsapps.com"
  },
  "routes": [
    {
      "pattern": "autodiscover.example.com",
      "custom_domain": true
    }
  ]
}

Then deploy:

pnpm run deploy

Option B: Via Cloudflare Dashboard

Keep wrangler.jsonc as-is (with keep_vars: true) and configure everything in the Dashboard:

1. Deploy the worker first: pnpm run deploy
2. Go to Workers & Pages → autodiscover-worker → Settings
3. Variables and Secrets → Add UPSTREAM with your mail service endpoint
4. Domains & Routes → Add custom domain autodiscover.example.com

The keep_vars setting in wrangler.jsonc ensures that subsequent deployments will not overwrite your Dashboard-configured variables.

3. Automated Deployment (Optional)

You can connect your forked GitHub repository to Cloudflare for automatic deployment on push:

1. Go to Workers & Pages → Create → Import a repository
2. Select your forked repository
3. Set Build command to pnpm install && pnpm run deploy
4. Configure environment variables and custom domain in Dashboard as described in Option B

Testing

After deployment, verify the worker is proxying requests correctly:

# Send a test Autodiscover request
curl -s -o /dev/null -w "%{http_code}" \
  -X POST \
  -H "Content-Type: text/xml" \
  -d '<?xml version="1.0" encoding="utf-8"?>
<Autodiscover xmlns="http://schemas.microsoft.com/exchange/autodiscover/outlook/requestschema/2006">
  <Request>
    <EMailAddress>user@example.com</EMailAddress>
    <AcceptableResponseSchema>http://schemas.microsoft.com/exchange/autodiscover/outlook/responseschema/2006a</AcceptableResponseSchema>
  </Request>
</Autodiscover>' \
  https://autodiscover.example.com/autodiscover/autodiscover.xml

# Expected: 200 (or 401 if the upstream requires authentication)

Local Development

Create a .dev.vars file (not committed to git) for local environment variables:

UPSTREAM=autodiscover-service.mail.us-west-2.awsapps.com

Then start the local dev server:

pnpm dev

License

MIT