Sender not showing in the "From" field

When I go into the sent items folder and open a mail I have sent, the from field is empty. If I send a mail on behalf of someone it says "on behalf of ..." in the from field. Some of my colleagues have the same problem as me, when others do not. I want everybody to have the configuration as such that the senders name always appears in the "from" field (in sent items). Does anyone know how I can fix this "problem".. ?