rmail-delete-backward
rmail-delete-backward is an interactive compiled Lisp function in `rmail.el
'.
(rmail-delete-backward &optional COUNT)
Delete this message and move to previous nondeleted one.
Deleted messages stay in the file until the M-x rmail-expunge command is given.
Optional argument COUNT (interactively, prefix argument) is a repeat count;
negative argument means move forwards instead of backwards.
Returns t if a new message is displayed after the delete, or nil otherwise.