@type t() :: %ApolloSignal.Types.SendEmailResponse{
  audience_id: String.t() | nil,
  created_at: String.t(),
  id: String.t(),
  message_id: String.t() | nil,
  messages: [ApolloSignal.Types.BatchSendItemResponse.t()] | nil,
  scheduled_at: String.t() | nil,
  status: String.t()
}