mh-delete-yanked-msg-window-flag

mh-delete-yanked-msg-window-flag is a variable defined in `mh-e.el'.
Its value is

nil

Documentation:
*Non-nil means delete any window displaying the message.

This deletes the window containing the original message after
yanking it with C-c C-y to make
more room on your screen for your reply.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 7.0 of the MH-E package that is part of Emacs 22.1.