Read and edit incoming mail.
Moves messages into file named by `rmail-file-name' and edits that
file in RMAIL Mode.
Type C-h m once editing that file, for a list of RMAIL commands.
May be called with file name as argument; then performs rmail editing on
that file, but does not copy any new mail into the file.
Interactively, if you supply a prefix argument, then you
have a chance to specify a file name with the minibuffer.
If `rmail-display-summary' is non-nil, make a summary for this RMAIL file. (fn &optional FILE-NAME-ARG)