One major drawback using the CSV import option with BPOS is that you only can specify one (!) domain. Our customer has multiple domains (like almost any company) and it seems that I had to edit al the user settings manually. I found the solution.
Before :
You see, only the default @xyz.emea.microsoftonline.com has been added to the e-mail adress.
Now select multiple accounts in the admin console (you have to do that, selecting only one user will not work!):
Select multiple users
Hit Edit user properties
And you see the following screen :
Select the new domain, hit OK. And now change it back . You will see that the new domain has been added.
Just choose the default options!