Hi Jasson,
you will have to change the permissions in the exchange.sqlite3 of the users.
You can see the defaults via
sqlite3 -readonly exchange.sqlite3 <<< "SELECT * FROM permissions WHERE username = 'default'"
For a correct number in the permissions row (2048 by default) your best bet is to first apply those permissions to some user via outlook and then check the table for the number.
As a reference, tho not the official (as i forgot to reference where i looked them up), you can also look at this table for corresponding values.
EDIT: Note that you have to ADD all permissions values to get the correct number (forgot the term how this is called /รถ\ ), e.g. readany+freebusysimple+freebusydetailed should be 6145 if i'm not mistaken...