GW 6.5 No Internal Undeliverable Msg

I am running NW 6.0 SP4 and Group Wise 6.5 sp1. the problem I have is that when a users mistypes an internal email message they do not receive any type of invalid address or undeliverable. Example godzilla@domain.com is not a valid email address. If I send a message to godzilla@domain.com I receive no error message. Where do i enable this on the system?