{
  d,
  ifThen,
  otherwise,
}:
# Queue Management
# https://stalw.art/docs/mta/outbound/overview
{
  # Virtual Queues
  # https://stalw.art/docs/mta/outbound/queue
  virtual.default.threads-per-node = 100;
  virtual.admin.threads-per-node = 10;
  virtual.local.threads-per-node = 100;
  # Schedules
  # https://stalw.art/docs/mta/outbound/schedule
  schedule =
    let
      queue = {
        retry = [
          "1m"
          "2m"
          "5m"
          "10m"
          "15m"
          "30m"
          "1h"
          "2h"
        ];
        notify = [
          "1d"
          "3d"
        ];
        max-attempts = 15;
      };
    in
    {
      default = queue // {
        queue-name = "default";
      };
      admin = queue // {
        queue-name = "admin";
      };
      local = queue // {
        queue-name = "local";
      };
    };
  # Routes
  # https://stalw.art/docs/mta/outbound/routing
  route = {
    local.type = "local";
    remote = {
      type = "mx";
      ip-lookup = "ipv6_then_ipv4";
      tls.implicit = false;
      tls.allow-invalid-certs = false;
    };
  };
  # Strategies
  # https://stalw.art/docs/mta/outbound/strategy
  strategy = {
    schedule = [
      (ifThen "is_local_domain('', rcpt_domain)" "'local'")
      (ifThen "source = 'dsn'" "'admin'")
      (ifThen "source = 'report'" "'admin'")
      (ifThen "source = 'autogenerated'" "'admin'")
      (otherwise "'default'")
    ];
    route = [
      (ifThen "is_local_domain('', rcpt_domain)" "'local'")
      (otherwise "'remote'")
    ];
    connection = "'default'";
    tls = "'default'";
  };
  # Remote Connection
  # https://stalw.art/docs/mta/outbound/connection
  connection.default = {
    ehlo-hostname = d.extUrl;
    source-ips = d.extIPs;
    timeout = {
      connect = "3m";
      greeting = "3m";
      ehlo = "3m";
      mail-from = "3m";
      rcpt-to = "3m";
      data = "10m";
    };
  };
  tls.default = {
    dane = "optional";
    mta-sts = "optional";
    starttls = "optional";
    allow-invalid-certs = false;
    timeout.tls = "3m";
    timeout.mta-sts = "3m";
  };
}