The mail delivery system has been altered to "bounce" messages to accounts that are inactive, deactivated, or scheduled to be deleted. This change has been made both because of user requests, and an interest to stop filling up our disks with spam that will never be read.
This is implemented in the MDA (procmail), by querying the passwd field of the target user's NIS entry. Those with the fields being set to *DEACTIVATED*, *DELETED*, or *INACTIVE* return EX_UNAVAIL, with an appropriate error message set, such as "This account has been deactivated." Administratively locked accounts (*LK*) are not affected by this change.