mh-mime-save-parts-default-directory

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

t

Documentation:
Default directory to use for K a.

The default value for this option is "Prompt Always" so that
you are always prompted for the directory in which to save the
attachments. However, if you usually use the same directory
within a session, then you can set this option to "Prompt the
First Time" to avoid the prompt each time. you can make this
directory permanent by choosing "Directory" and entering the
directory's name.

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.