@spec download(Pop3mail.EpopDownloader.Options.t()) ::
  {:ok, integer()} | {:error, atom()}

Read all emails and save them to disk.

options - EpopDownloader.Options

@spec parse_process_and_store(
  String.t(),
  integer(),
  boolean() | nil,
  boolean(),
  String.t()
) ::
  {atom(), String.t()}
  | [{:ok, String.t()} | {:error, atom(), String.t()}]
  | {:skip, [{:header, String.t(), String.t()}]}

Parse headers, decode body and store everything.

• mail_content - string with the complete raw email message.
• mail_loop_count - number of the email in the current session.
• delivered - true/false/nil. Presence, absence or don't care of the 'Delivered-To' email header.
• save_raw - true/false. Save or don't save the raw email message.
• output_dir - directory where all emails are stored.

@spec retrieve_and_store(
  epop_client_type(),
  integer(),
  Pop3mail.EpopDownloader.Options.t()
) ::
  {atom(), String.t()}
  | [{:ok, String.t()} | {:error, atom(), String.t()}]
  | {:skip, [{:header, String.t(), String.t()}]}

Retrieve, parse and store an email.

• epop_client - client returned by :epop_client.connect function.
• mail_loop_counter - number of the email in the current session.
• options - EpopDownloader.Options

@spec retrieve_and_store_all(epop_client_type(), Pop3mail.EpopDownloader.Options.t()) ::
  {:ok, integer()}

Read all emails and save them to disk.

• epop_client - client returned by :epop_client.connect function.
• options - EpopDownloader.Options