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command line email with aerc

Posted on 2020-05-04 - 7 min read
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I just set up command line email with my new work account and my ProtonMail account today! This article will be covering the full setup.

aerc screenshot

setting up proton-bridge

ProtonMail is an email service that end-to-end encrypts its users' emails with PGP. As a result, it doesn't speak SMTP or IMAP directly, since email clients wouldn't know how to undo the encryption anyway. That's why they've provided proton-bridge, a (now) open-source SMTP/IMAP server that translates their own API calls into SMTP/IMAP for your email clients. For security, it's best to run this locally, so that emails aren't exposed over the network after they're decrypted.

For my setup, I have proton-bridge running as a systemd service. That means we have to deal with any interactive parts of the service so they're not popping up anymore.

Firstly, we want to build the bridge without support for the GUI. We won't be using it anyway, so this eliminates the Qt dependency.

Secondly, proton-bridge stores keys in an encrypted keyring, like [password-store][5]. My regular password-store is encrypted with my passphrase-protected GPG key, so I didn't want to use it since it'll be asking me for the passphrase again every time the timeout expires. We're going to make a separate GPG and password-store setup that will only be used for proton-bridge. Since it's all running locally anyway, we're not to use a passphrase on this GPG key.

Authenticating only happens once, and the local SMTP/IMAP password doesn't change very often, so we won't really care about that. We'll bundle this up into a couple of nice scripts and then have it configured to start on startup!

building proton-bridge

To build proton-bridge without the GUI, we'll need to grab a copy of the source. Clone the repo and then change directory to it:

git clone https://github.com/protonmail/proton-bridge
cd proton-bridge

As of now, there's no tagged releases, so let's just build straight from master. Peeking into the Makefile, there isn't a release build for the nogui option, so let's add it ourselves. Put this somewhere in the Makefile:

    PROTONMAIL_ENV= go build ${BUILD_FLAGS_NOGUI} ./cmd/Desktop-Bridge

Then run make build-nogui and you should get a binary called Desktop-Bridge. Don't authenticate just quite yet; we want to set up the keychain first so it stores it in the right place.

isolating the keychain

proton-bridge needs a keychain to store the keys that it gets from authenticating. The bridge supports [password-store][5] and GNOME keyring, but I'll be setting up password-store here. The goal now is to create a password-store instance that's isolated from the default installation so it doesn't require any interactive prompts.

For this part, I created two directories: the directory for the new GPG homedir, and the directory for the new password-store. If you're copy-pasting commands out of this post, I'd recommend you add these variables right now:

export PASSWORD_STORE_DIR=/path/to/password/store
export GNUPGHOME=/path/to/gpg/home

...obviously replacing the paths with paths that you choose. These variables are used by pass and gpg to overwrite the default directories they use, so it's important to set them up. The next step is to make sure they both exist:


Now initialize the GPG key first. Run:

gpg --full-generate-key

There should be an interactive prompt. Go through and answer the questions however you see fit. I'd recommend you make the key 4096 bits, never expire, and have no passphrase. This key should never leave your local machine, and you will almost never use it directly, so there should be no problem.

Then, set up password-store. Run:

pass init [gpg-id]

where [gpg-id] is some identifier for the key you just created (name or email works).

At this point, you should test your configuration by running the Desktop-Bridge program with the -c option to open the prompt. Make sure you are able to log in and that rerunning the program should automatically run the bridge using the authenticated user without any interactive prompts.

            Welcome to ProtonMail Bridge interactive shell
    ^^                __..-:'':__:..:__:'':-..__
                  _.-:__:.-:'':  :  :  :'':-.:__:-._
                .':.-:  :  :  :  :  :  :  :  :  :._:'.
             _ :.':  :  :  :  :  :  :  :  :  :  :  :'.: _
            [ ]:  :  :  :  :  :  :  :  :  :  :  :  :  :[ ]
            [ ]:  :  :  :  :  :  :  :  :  :  :  :  :  :[ ]
   :::::::::[ ]:__:__:__:__:__:__:__:__:__:__:__:__:__:[ ]:::::::::::
   !!!!!!!!![ ]!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!![ ]!!!!!!!!!!!
   ^^^^^^^^^[ ]^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^[ ]^^^^^^^^^^^
            [ ]                                        [ ]
            [ ]                                        [ ]
      jgs   [ ]                                        [ ]
    ~~^_~^~/   \~^-~^~ _~^-~_^~-^~_^~~-^~_~^~-~_~-^~_^/   \~^ ~~_ ^
>>> login
Username: iptq
Authenticating ...
Adding account ...

automating the whole process

Now that the bridge is able to run independently, let's make a tiny wrapper script called run-proton-bridge.sh that calls it using the appropriate environment variables:


# same as before
export PASSWORD_STORE_DIR=/path/to/password/store
export GNUPGHOME=/path/to/gpg/home

exec /path/to/Desktop-Bridge $@

Save this somewhere, give it executable permissions.

Finally, we can add a systemd service that runs this whole business whenever the network is available. I'd recommend adding this as a user service rather than a system service. You can put this somewhere like $HOME/.config/systemd/user/proton-bridge.service:




Run this service:

systemctl --user start proton-bridge

Enable it to have it auto-start:

systemctl --user enable proton-bridge

Bridge configuration should be complete at this point, so let's move on to configuring our mail client to work with it.

setting up aerc

aerc is a new (work-in-progress) command-line mail client by Drew Devault. It features a familiar set of default keybinds, calls out to your favorite editor for composition, and DWIM for many other things. I just started using it today and had no problem getting used to the interface.

The setup for basic SMTP/IMAP email accounts is actually pretty trivial. When you run aerc for the first time, or whenever you run the command :new-account, an interactive screen is brought up prompting you for the details about your mailbox. If your mail provider doesn't work immediately, jump into #aerc on freenode; the folks there are super helpful with different mail providers.

setting up aerc.. with protonmail

If you've been keeping up, then all the pieces should be in place for aerc to work with ProtonMail. There's just a tiny bit of glue we have to add to put it all together.

aerc does not allow untrusted certificates. Since proton-bridge generates a self-signed cert, we'll need to trust this cert before we can do anything. There's not really an easy way to pull the certificate out, so I'd recommend just firing up the bridge and then connecting to it using the openssl client and then copy-pasting the certificate part:

$ openssl s_client -starttls imap -connect -showcerts
Can't use SSL_get_servername
depth=0 C = CH, O = Proton Technologies AG, OU = ProtonMail, CN =
verify return:1
Certificate chain
 0 s:C = CH, O = Proton Technologies AG, OU = ProtonMail, CN =
   i:C = CH, O = Proton Technologies AG, OU = ProtonMail, CN =
Server certificate
subject=C = CH, O = Proton Technologies AG, OU = ProtonMail, CN =
issuer=C = CH, O = Proton Technologies AG, OU = ProtonMail, CN =

Take that huge chunk starting with the line BEGIN CERTIFICATE and ending with the line END CERTIFICATE and stick it into some file (ex. protonmail.crt). This is the self-signed cert we need to trust.

Now we'll need to tell our system to allow this cert. This varies from system to system; I'm on an Arch machine, so I ran:

sudo trust anchor --store protonmail.crt

After this, fire up aerc again, and your emails should start showing up.

End. This post is tagged with: setup , email , protonmail

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written by michael zhang. source