@type t() :: %Sendio.Emails.Email{
  attachments: [Sendio.Emails.Attachment.t()] | nil,
  bcc: [String.t()] | nil,
  cc: [String.t()] | nil,
  created_at: DateTime.t() | nil,
  from: String.t() | nil,
  headers: map(),
  html: String.t() | nil,
  id: String.t(),
  last_event: String.t() | nil,
  reply_to: String.t() | nil,
  scheduled_at: DateTime.t() | nil,
  subject: String.t() | nil,
  tags: [Sendio.Emails.Tag.t()] | nil,
  text: String.t() | nil,
  to: [String.t()] | nil
}