@type t() :: %Paubox.Message{
  allow_non_tls: :boolean,
  attachments: [Paubox.Attachment.t()] | nil,
  bcc: [String.t()] | nil,
  cc: [String.t()] | nil,
  force_secure_notification: :boolean,
  from: String.t(),
  html_content: String.t() | nil,
  recipients: [String.t()] | nil,
  reply_to: String.t() | nil,
  subject: String.t(),
  text_content: String.t() | nil,
  unsubscribe: String.t() | nil
}