Exchange 2007 IP allow List feature enable connection from list of IP addresses to exchange.
This list will disregard RBLs and will bypass any filters on the way.

One way of doing it shortly is using cmdlet from exchange shell:
Add-IPAllowListEntry –IPAddress or use -IPRange

Other way of doing it is using the Exchange Manager:

1. Select Hub Transport On exchange 2007 Server manager under Configuration node.
2. Mark the Hub Transport server on the details pane.
3. Click the Anti-spam tab.
4. Click IP Allow List.
5. In the right Actions pane, select the Properties link.
6. Select the Allowed Addresses needed tab and click Add.
7. Add the IP address or range.
8. Click OK for all windows.