Has this always been the case, or just when a trusted domain is in the CC address?
From this example trusted.com was masked even though the sender was in a trusted domain, but the cc: address was not masked. This email was received within the last week.
from: Jane <*****.*****.*****.*****#trusted.com@ob.0sg.net>
to: "*****.##.*****@xoxy.net" <*****.##.*****@xoxy.net>
cc: John <*****@trusted.com>
subject: ***** ***** (trusted: trusted.com )
CTJ