My two cents on this , if you are still facing authentication failure from javamail trying to connect to mailbox and read emails, First and foremost make sure the application setup in azure active directory has below permissions.
IMAP.AccessAsApp
Mail.Read
Mail.Send (For Sending)
Secondly, Create service principal with the enterprise application id as mentioned in the original post.
Once done check here if your generated token has all the roles you have assigned.
Even if you assigned necessary roles and you can able to connect to mailbox via powershell still you might get AUTHENTICATE failed from javamail because you might be using this property (mail.imap.auth.mechanisms) wrongly , replace mail.imap with mail.imaps and it should solve the problem.
"mail.imaps.auth.mechanisms"="XOAUTH2"
"mail.imap.host"="outlookoffice365.com"
"mail.smtp.port"=993
"mail.store.protocol"="imaps"
session.getStore("imaps")
store.connect(host,port,user,token)
Good luck !!
