If the -mbox switch is given (the default), then the messages are separated using mbox (uucp) style delimiters. This is the format used by most mail clients (elm, mailx, etc.).

If the -mmdf switch is given, then the messages are separated by mmdf style delimiters. Each message in the file is separated by four CTRL-A's and a newline.

rcvpack will correctly lock and unlock the file to serialize access to the file, when running multiple copies of rcvpack .

In general, its use is obsoleted by the file action of slocal, although it might still have occasional uses in various shell scripts.