[horde] Change default mail "folder" directory

[José Luís Ramos]

Hello.
Can you help me with the following  question?
How can i set the default mail directory of users to /home/<user>/mail,
instead of /home/<user>? 

When I select "Open Folder", in Horde/Imp,  it displays all the files in the
user home dir, and not in the "/home/<user>/mail" dir.
 I set up the option 'folders' => 'mail/', in the
".../horde/imp/config/servers.php" file but it does not work.
(The former installation of horde.2.X worked this way.)

Thanks.

José Luís