mh-store-default-directory

mh-store-default-directory is a variable defined in `mh-e.el'.
Its value is

nil

Documentation:
*Default directory for X u.

If you would like to change the initial default directory,
customize this option, change the value from "Current" to
"Directory", and then enter the name of the directory for storing
the content of these messages.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 6.0 of the MH-E package that is part of Emacs 22.1.