Selecting YES does remove all the data and settings.
You can check this for yourself by going to that folder after uninstall.
I had to restore my old Outlook Express dbx files to my current version of eM Client, 8.1.979. Like Marine about 4 years ago, all the folders appeared but the following was noted:
my existing empty local folders, Inbox, Outbox, Sent, Trash, Drafts had their mail items imported from the dbx files;
A second local folders then appeared below the first set of local folders, which contained all the sub-folders in the Deleted and Inbox of the original outlook express mailbox;
There were no mail items in these sub-folders. All the mail items were in in a sub-folder with no name, see screen shot…
What is the explanation and is there a way to re-import all mail items into sub-folders of the first local folder?
Sorry but I could not find a more recent post on this matter.