[otrs] Automatically update customer data upon incoming email

I've managed to get the synchronization working with AD when I'm creating tickets myself. Then I can retrieve all the fields I've defined for the customer. But when one of the customers in the AD database sends an email to the system, those fields aren't updated at all. If I go to "Customer" and then just search for the customer that's already been entered in the fields by the email, everything works as expected. How can I automatically update these customer fields when the user sends an email? Marius