Fast Mail Proxy

Or Fox Mail Proxy, depending on if you want to be cute :3.

About

Fast Mail Proxy is a simple mail proxy that uses email apis to act as a transparent proxy.

Mail can be sent as well as received through the proxy by using special addresses

Backstory

A while back, I was excited to use cloudflare's mail forwarding, however, when I used it, I discovered that it can only forward mail and not act as a true proxy. Sending mail through it and keeping anonymity while replying was impossible.

This was an issue for me as I wanted something privacy preserving like duck's email proxy, where mail can be sent through the proxy and be sent out under a vanity address.

This project is a implementation of what I hope that I could get from cloudflare's email forwarding service, as well as the ability to semi self host a email proxy service.

Setting up

Fast Mail Proxy can accept any kind of mail, as long as the relevant handlers are defined. The current default handler is mailgun.

Non serverless environments

Edit users.json and you are good to go!

Serverless environments

Users need to be set manually by pushing to kv storage.

NO_DISK as well as DECRYPT_KEY needs to be set as well.

To create and namespace, check out this piece of documentation by cloudflare

Options

Server options

INTEGRATION: The handler to load, defaults to mailgun

RECEIVE_ENDPOINT: The webhook's listening endpoint, defaults to /api/receive-mail

NO_DISK: Disable disk writes, defaults to false,

DECRYPT_KEY: Server's decryption key in hex format. Usually set if there isn't disk write access.

DEFAULT_NAME: Sender's default name if the script fails to extract it. Defaults to No Name

MAILER_DOMAIN: The domain in which mail is configured to be sent from. Must be set.

Mailgun options

Most keys can be found in this article by mailgun

MAILGUN_API_KEY: Mailgun's api key

MAILGUN_WEBHOOK_SIGNING_KEY: Mailgun webhook signing key, used for verification.

MAILGUN_API_ENDPOINT: Mailgun's api endpoint, change if your account is in europe. Default is https://api.mailgun.net

How does it work?

The directory how-it-works explains how the proxy functions.

Receiving

To receive mail, configure users.json and set the alias for your email. There is an example file in users.json.sample

All mail that gets sent to the address will be forwarded to the configured email.

Sending

The to address field will have to be modified accordingly (Check out function wrap and unwrap for the exact process in modules/utils.js)

To manually wrap the address, here are the steps

1. Replace @ with _at_
2. Add on your alias to the back prefixed with an underscore. For example, a user with alias fox will have to add on _fox to the back of the address
3. Add on your mailing domain

So, if you want to send a email as fox@proxy.com, where fox is the alias and proxy.com is the mailer domain to wolf@forrest.com, the to address will look like this

wolf_at_forrest.com_fox@proxy.com

(Using foxes and wolfs are more cute and interesting than the overused alice and bob. Fight me if you don't like it.)

Sending mail requires a alias as the proxy needs to know who to address as well as to check if the sender owns the alias.

Future features

• Cloudflare workers support using cloudflare kv storage
• Generic serverless support

*Serverless support might have some issues where large attachments will cause a timeout.