[otrs] CustomerID not being set anymore

Hi there, I recently updated from 5.0.9 to 5.0.16, after which I noticed an unwanted change in behaviour: The system used to set the CustomerID to the e-mail address a message was received from. After the update, the field CustomerID remains empty. I looked around in the system settings but could not find anything that might be related to it. I also did not find any mentions of it being changed in the release notes. Of course, I copied the configuration file to the new installation folder (as described in the update manual). Does anyone know how to restore the previous behaviour? Cheers, Kai