In evolution 2.8.0 I am unable to create a new maildir or MH account.
The problem is that the widget for selecting the 'path' is expecting
a file name, whereas maildir and MH require a directory name.

From mail-config.glade:
===========================
<widget class="GtkFileChooserButton" id="source_path_entry">
        <property name="visible">True</property>
        <property name="title" translatable="yes">Mailbox location</property>
        <property name="action">GTK_FILE_CHOOSER_ACTION_OPEN</property>
        <property name="local_only">True</property>
        <property name="show_hidden">False</property>
        <property name="do_overwrite_confirmation">False</property>
        <property name="width_chars">-1</property>
</widget>
============================

The GTK_FILE_CHOOSER_ACTION_OPEN should be
GTK_FILE_CHOOSER_ACTION_SELECT_FOLDER
if you want to select a directory.  I expect this widget is currently
used for both mbox and maildir configuration, so the required change
won't be a one-liner.

(aside: this isn't the first regression affecting mh backends...
not everyone is using mbox.)