SMTP Source Address Preservation

Ive seen a great number of posts around this thread already, but none (that I have found) provide a workable solution to the following key points:

1) Preserve the Source IP to allow the Connectors deployed across Exchange Servers to allow/deny the connection (based on a preconfigured White List).

2) The Exchange Servers Default Gateway is that of all other devices on the subnet, and not that of the F5.

Thanks for any help or suggestions.