cf-email-fanout-ts

TypeScript Cloudflare Email Worker that forwards inbound email for your domain to multiple verified Cloudflare destination addresses.

What it does

• Accepts inbound mail routed to a Cloudflare Email Worker.
• Fans the message out to multiple verified destination mailboxes.
• Optionally prefixes the subject with the alias used.
• Adds X-Original-Rcpt-To and X-Original-Mail-From headers for downstream filtering.
• Supports basic allow/deny recipient and sender-domain controls.
• Rejects suspicious mail loops.

Repo layout

cf-email-fanout-ts/
├─ .github/
│  └─ copilot-instructions.md
├─ src/
│  └─ index.ts
├─ package.json
├─ README.md
├─ tsconfig.json
└─ wrangler.toml

Requirements

• Cloudflare account with your domain already using Email Routing.
• Three verified Cloudflare destination addresses already configured.
• Node.js 20+ recommended.
• npm.

Quick start

npm install
npx wrangler login
npx wrangler deploy

Configure destinations

Edit wrangler.toml:

[vars]
FORWARD_TO = "you1@example.com,you2@example.com,you3@example.com"
ADD_SUBJECT_PREFIX = "true"
SUBJECT_PREFIX_MODE = "alias"
ALLOW_RECIPIENTS = ""
DENY_RECIPIENTS = "abuse@yourdomain.com,postmaster@yourdomain.com"
ALLOWED_SENDER_DOMAINS = ""
DENIED_SENDER_DOMAINS = ""
MAX_MESSAGE_SIZE_BYTES = "20971520"

Variable meanings

• FORWARD_TO: comma-separated verified destination inboxes.
• ADD_SUBJECT_PREFIX: true or false.
• SUBJECT_PREFIX_MODE: alias gives [shopping], full gives [shopping@yourdomain.com].
• ALLOW_RECIPIENTS: optional comma-separated exact destination aliases to allow.
• DENY_RECIPIENTS: optional comma-separated exact aliases to reject.
• ALLOWED_SENDER_DOMAINS: optional sender domain allow-list.
• DENIED_SENDER_DOMAINS: optional sender domain deny-list.
• MAX_MESSAGE_SIZE_BYTES: optional size cap.

Cloudflare dashboard steps

1. Deploy the worker with npx wrangler deploy.
2. Open Cloudflare Dashboard.
3. Select your domain.
4. Go to Email or Email Routing.
5. Open Email Workers or the route creation flow.
6. Create a route.
7. Set the custom address or broader route pattern you want routed into the worker.
8. Choose your deployed worker cf-email-fanout-ts as the destination.
9. Save the route.
10. Send test mail to one or more aliases on your domain.

Suggested first tests

Send messages to:

• shopping@yourdomain.com
• banking@yourdomain.com
• random-test-123@yourdomain.com

Then verify:

• all three destination inboxes received the message,
• the subject prefix is present if enabled,
• X-Original-Rcpt-To is visible in headers,
• loop detection is not firing unexpectedly.

Useful commands

npm run check
npm run deploy
npm run tail

Notes

• Email Worker behavior is best tested by sending real mail through Cloudflare Email Routing.
• Downstream mail clients vary in how visibly they surface original recipient headers.
• Catch-all style routing is powerful, but also excellent at inviting spam to dinner.