mh-summary-height

mh-summary-height is a variable defined in `mh-e.el'.
Its value is

nil

Documentation:
*Number of lines in MH-Folder buffer (including the mode line).

The default value of this option is "Automatic" which means
that the MH-Folder buffer will maintain the same proportional
size if the frame is resized. If you'd prefer a fixed height,
then choose the "Fixed Size" option and enter the number of
lines you'd like to see.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 7.4 of the MH-E package that is part of Emacs 22.1.