Okay sorry ! Haven't checked the config.inc.php file.
To download a folder, all I could see is to click on the cog-wheel at the bottom of the folder column.
And to download a selection of mail, I found out that after clicking a selection of mails and then on the "MORE" button in the "icon menu", I was offered to download them (just the same way as it is when clicking on a single mail)
Is this what you were looking for ?