Config format

A typechecked Dhall record

The config is a Dhall record — aliases, domains, relay, limits, storage, DKIM keys — typechecked against its schema before the daemon binds a port. Config errors (bad types, unknown fields) are caught at startup, not at 3 a.m. when mail bounces.

let Auth = { enabled : Bool, username : Text, password : Text }
in  let Config =
      { hostname : Text
      , domains : List Text
      , listen : { address : Text, port : Natural }
      , limits : { message : Natural, line : Natural, rcpts : Natural
                 , cmd_timeout : Natural, data_timeout : Natural }
      , relay : { host : Text, port : Natural, auth : Auth, retries : Natural
                , tls : Text, tls_ca : Text, max_attempts : Natural }
      , storage : { path : Text, spool : Text, retention_days : Natural }
      , reply : { prefix : Text, separator : Text }
      , catch_all : Text
      , aliases : List { alias : Text, destinations : List Text }
      , http : { address : Text, port : Natural }
      , admin : { token : Text }
      , dkim : List { domain : Text, selector : Text, private_key : Text }
      }
in  { hostname = "mx.example.com"
    , domains = [ "example.com" ]
    , listen = { address = "0.0.0.0", port = 2525 }
    , limits = { message = 26214400, line = 1000, rcpts = 100
               , cmd_timeout = 300, data_timeout = 600 }
    , relay = { host = "127.0.0.1", port = 2526
              , auth = { enabled = False, username = "", password = "" }
              , retries = 3, tls = "none", tls_ca = "", max_attempts = 100 }
    , storage = { path = "./var/db", spool = "./var/spool", retention_days = 30 }
    , reply = { prefix = "reply", separator = "+" }
    , catch_all = ""
    , aliases = [ { alias = "jane@example.com", destinations = [ "jane@realmail.example" ] }
                , { alias = "shopping@example.com", destinations = [ "jane@realmail.example", "bob@realmail.example" ] }
                ]
    , http = { address = "127.0.0.1", port = 8080 }
    , admin = { token = "change-me" }
    , dkim = [] : List { domain : Text, selector : Text, private_key : Text }
    } : Config

relay.tls is none, starttls, or starttls-verify. An empty tls_ca uses the embedded Mozilla CA bundle (only consulted when tls == starttls-verify). admin.token is the bearer token for the admin HTTP API — a real deployment must use a long random token (a 500-char ceiling is enforced).