@type t() :: %ApolloSignal.Types.SendEmailRequest{
  attachments: [ApolloSignal.Types.AttachmentRequest.t()] | nil,
  bcc: [String.t()] | nil,
  cc: [String.t()] | nil,
  delivery_window: ApolloSignal.Types.DeliveryWindowRequest.t() | nil,
  from: String.t(),
  html: String.t() | nil,
  idempotency_key: String.t() | nil,
  metadata: %{optional(String.t()) => String.t()} | nil,
  reply_to: String.t() | nil,
  scheduled_at: String.t() | nil,
  send_time_category: String.t() | nil,
  subject: String.t() | nil,
  tags: %{optional(String.t()) => String.t()} | nil,
  test_mode: boolean() | nil,
  text: String.t() | nil,
  to: [String.t()],
  tracking_settings: ApolloSignal.Types.TrackingSettingsRequest.t() | nil
}