To download e-mails, go to roundcube. Select
all the mails you want to transfer to the new mailbox. Then click
on the download button for .zip format.
Now you are going to upload all e-mails to the new mailbox. Go to the same menu with the 3 dots.
Go to import and upload the .zip file. All mails will be in the new mailbox from that moment on.
Please note! The mailbox in this tutorial is set to Dutch.