Read here: http://spf.pobox.com/howworks.html Perimeter IP list/range are the IPs of machines delivering inbound mail to you which will not be checked for SenderID compliance. You could also think of this as a "whitelist". -----Original Message----- From: Andrew English [mailto:andrew@xxxxxxxxxxxxxxxxxxxxxx] Sent: Sunday, October 23, 2005 8:18 AM To: [ExchangeList] Subject: [exchangelist] Exchange SP2 How does the new features for Exchange Message Delivery system works. Secure ID Filtering; what does this do exactly? Does it ask the sender to send a request to the exchange user to be added to his accepted list or am I thinking of something completely different? And I am not sure what Perimeter IP List and IP Range Configuration does? Thanks Andrew