xC0000005 -
We have a rule that blocks mail coming in on external interface (from the internet) that has our internal domain name listed in the sender. (i.e. anyone sending us mail from outside our organization purporting to be FROM our domain name). That continued working fine. However, we also have an exception in that rule that says if the "FROM:" in the message header contains certain text, to allow the mail through. We have this because we are on a large campus with numerous list servers that need to bypass this filter.
After applying RU9, the block of external messages with our domain name continued to work, but the excpetions stated in the rule did not. Hope that makes sense..