feat: reorganise link docs and add proton mail

docs/link/channels/proton.md

@@ -0,0 +1,65 @@
+---
+title: Proton Mail Channel
+sidebar_label: Proton Mail Channel
+sidebar_position: 55
+description: Using a ProtonMail email account
+---
+
+[Proton Mail](https://proton.me/mail) is the largest end-to-end encrypted email hosting service.
+It was launched in 2014 and is headquartered in Geneva, Switzerland.
+It is owned by the non-profit Proton Foundation through its subsidiary Proton AG.
+Proton Mail uses client-side encryption to protect email content and user data before they are sent to Proton Mail
+servers, unlike other common email providers.
+
+The source code for the back end of Proton Mail remains closed-source, but Proton Mail released the source code for the
+web interface, iOS and Android apps, and the [Proton Mail Bridge app](https://github.com/ProtonMail/proton-bridge)
+under an open-source licence.
+
+Although Proton Mail's encryption uses the open standard OpenPGP, and the Link platform support OpenPGP when used with
+other email providers, it is not possible to directly interact with the encryption from the Link platform.
+This is because Proton Mail does not provide the traditional IMAP and SMTP server endpoints to send and receive emails
+and only allows connection via the Proton Mail bridge app which handles all encryption and decryption of messages.
+
+## Requirements
+
+* You must have a paid plan to use the Proton Mail channel as the use of the Proton Mail Bridge app is not possible on
+a free account.
+* Additionally, a user must be dedicated for the use of the helpdesk, it is not sufficient to create an alias on an
+existing user.
+
+## Encryption & Key Management
+
+OpenPGP private keys are created automatically for each Proton Mail account, although these are stored in a way that
+they are not generally available other than when successfully authenticated to the platform.
+In the case of Link, this means that the Proton Mail Bridge app is authenticated and then has access to the OpenPGP
+private key.
+
+It is not currently possible to import public keys of 3rd-party (i.e. non-Proton Mail) email addresses, and so only
+emails between Proton Mail users will be end-to-end encrypted.
+The service also
+[does not support the Autocrypt standard](https://protonmail.uservoice.com/forums/945460-general-ideas/suggestions/32845105-autocrypt-support),
+which allows other clients to import discovered public keys automatically on new conversations.
+The Proton Mail documentation [has more on this topic](https://proton.me/support/proton-mail-encryption-explained).
+
+We will provide you with your public OpenPGP key when the channel is set up, and you can make this discoverable via your
+website, but for conversations with 3rd-party accounts we expect the conversations will only be encrypted in one
+direction and your replies will not be encrypted.
+
+The helpdesk is unaware of the encryption happening in Protonmail, and cannot inform agents when an email that was sent
+or received by the helpdesk was encrypted or not.
+
+## Setting up
+
+If you do not have an organisational account, we can fully manage the Proton Mail account setup including billing.
+Please [contact us](https://www.sr2.uk/contact) to discuss this.
+
+If you have an organisational account,
+[send an invite for the new user](https://proton.me/support/add-users-organization#create-a-new-user) (the new helpdesk
+channel address) to contact@sr2.uk, and email the same address to let us know you are doing this and that you would
+like the channel added to your helpdesk.
+
+Once the setup is complete we will provide you with OpenPGP public key and will also upload it to
+[keys.openpgp.org](https://keys.openpgp.org/) to aid in its discovery by users.
+We can also provide support on setting up Web Key Discovery (WKD) on your custom email domain if desired to further
+increase the chances that inbound emails will be automatically encrypted, although this still cannot help to encrypt
+replies to 3rd-party email services.