VM provides a special form of undo which allows changes to message attributes to be undone.
Typing C-x u or C-_ (
vm-undo) undoes the last
attribute change. Consecutive
vm-undo's undo further and further
back. Any intervening command breaks the undo chain, after which the
undos themselves become undoable by subsequent invocations of
Note that expunges, saves and message edits are not undoable.