Envirnonment: 1 Exchange 2003, 1 Exchange 2007 hub/mailbox, 1 2007 CAS.Currently all external mail coonnections go through the old 2003 server.I have addedan additionalIP and Receive connector on the Hub that will be used by app servers to relay to the outside world.I will be creating a new Send connector that will use an appliance in the DMZfor SMTP gateway.My question is, I need to create firewall rules from internal(Exchange) to dmz(Aplliance). Will the Send connector always use the same IP? How does it determine which IP will be used? If an app server connects on the realy IP, will the Send Connector use that IP to connect to the external appliance. Can I bind an IP to the Send Connector?Thanks

Yes, you can bind the send connector with IP address to send mails. Refer below article for further understanding and let us know if you have any doubt... How to Configure Internet Mail Flow Through Exchange Hosted Services or an External SMTP Gateway http://technet.microsoft.com/en-us/library/bb738161.aspx Amit Tank | MVP Exchange Server | MCITP: EMA | MCSA: M | http://ExchangeShare.WordPress.com

In this article, i don't see any info that specifies which IP will be used for the Send Connector. I have two interfaces, two IP's on the box. Without binding the Connector to the IP, how do I know which one it will use?

Oh you mean local IP. I didn't see any way to bound the local IP address unless you have send connector on Edge transport server, on Edge server you can useSourceIPAddress parameter to define the local IP address which should be used... Set-SendConnector http://technet.microsoft.com/en-us/library/aa998294.aspxAmit Tank | MVP Exchange Server | MCITP: EMA | MCSA: M | http://ExchangeShare.WordPress.com