mbrts/README.md

# mbrts

Real-time mail delivery for maildirs via Fastmail's JMAP push API.

Connects to Fastmail's JMAP EventSource stream and delivers new messages directly to a local Maildir the moment they arrive without polling.

## How it works

On first run, or when the saved JMAP state is stale, mbrts falls back to `mbsync` for a full sync, then takes over from that point.

## Setup

Create a Fastmail API token at **Settings → Security → API Tokens**.

### Config file

By default mbrts reads `$XDG_CONFIG_HOME/mbrts/config.yaml` (e.g. `~/.config/mbrts/config.yaml`):

```yaml
accounts:
  - name: Personal
    maildir_path: /home/you/.mail/Personal
    password_command: "pass show fastmail/api-token"
```

Each account requires exactly one token source:

| Field | Description |
|---|---|
| `password_command` | Shell command that prints the token to stdout |
| `token_file` | Path to a file containing the token |
| `token_env` | Name of an environment variable containing the token |

Optional fields: `mbsync_account` (mbsync channel/group name; defaults to `name`), `log_level` (top-level: `debug`, `info`, `warn`, `error`).

### CLI flags

Every config file option has an equivalent flag. Flags override the config file. A single account can be configured entirely on the command line without a config file:

```
mbrts --name Personal \
      --maildir-path ~/.mail/Personal \
      --password-command "pass show fastmail/api-token"
```

Run `mbrts --help` for the full flag list, or `mbrts --version` to print the version.

### Nix

Add mbrts as a flake input:

```nix
inputs.mbrts = {
  url = "git+https://code.adriano.fyi/me/mbrts";
  inputs.nixpkgs.follows = "nixpkgs";
};
```

The flake exposes:

| Output | Description |
|---|---|
| `packages.*.default` | The `mbrts` binary |
| `overlays.default` | Adds `pkgs.mbrts` |
| `homeManagerModules.default` | The `services.mbrts` home-manager module |

### home-manager module

Add the overlay and module to your home-manager configuration, then configure the service:

```nix
# in your flake outputs
overlays = [ inputs.mbrts.overlays.default ];

# in your home-manager module list
inputs.mbrts.homeManagerModules.default

# in your home-manager config
services.mbrts = {
  enable = true;
  accounts = [
    {
      name = "Personal";
      maildirPath = "/home/you/.mail/Personal";
      passwordCommand = "pass show fastmail/api-token";
    }
  ];
};
```

The module generates a config file and runs mbrts as a `systemd` user service. Logs are available via `journalctl --user -u mbrts -f`.

Module options:

| Option | Type | Default | Description |
|---|---|---|---|
| `enable` | bool | — | Enable the service |
| `package` | package | `pkgs.mbrts` | Package to use |
| `logLevel` | enum | `"info"` | `debug`, `info`, `warn`, or `error` |
| `accounts` | list | `[]` | List of account submodules (see config file fields above) |

## Build

```
CGO_ENABLED=0 go build -o mbrts .
```

## aerc

Configure the account source as `maildir://` so aerc picks up delivered messages immediately via inotify:

```ini
source = maildir:///home/you/.mail/Personal
```