It was actually quite straigt forward
I startet a "windows guest restore" of our exchangeserver so we had the .edg and log files from our exchange avaiable from c:\veeamflr
Then we add an Office 365 tenant, add store and chose Exchange and the .edb and .log files.
Marked the content we wanted to restarte and the mailbox and as typed in outlook.office365.com
All worked straight forward.