New Outlook, IMAP: emails always loaded from server

Today I tried "New Outlook" for MAC. I added some IMAP accounts without MS sync enabled and my folders got populated (I've some folders with over 100k emails).

It seems that New Outlook doesn't store emails in a database, after every restart of Outlook all messages get fetched from my IMAP server. This causes problems around being able to search emails.

Is this behaviour expected or do I've to configure anything to "cache" locally?