Login to MailSuite.
Click [Folders] at the top left of the screen.
Click the [Backup] button of the folder to back up.
Save the created zip file locally on your PC. It is automatically named as ”foldername.zip”(*1). It contains multiple .eml files. One .eml file is created for each e-mail.
On Thunderbird, create a folder (*2) with an appropriate name under ECCS Cloud Mail or a local folder on the PC.
Select multiple [up to several hundred] eml files in *1.
Drag and drop the selected range to *2.