Double SNAT for SMTP traffic

Hello,

 

lets start with a picture, cause it's worth a thousand words...

 

 

We've got this kinda weird architecture of SMTP traffic:

 

SMTP server has whitelist of IP addresses which contains only IP2 (10.0.0.20). All servers (there is a lot more than these two) are configured to use IP1 (10.0.0.10) as gateway when routing to mailhost, because they are not on the whitelist and can't talk to SMTP server directly.

 

I have to move this concept onto F5 BigIP LoadBalancer (put F5 in Alteon's place) without any changes made to servers and SMTP server. All I could accomplish by now was simple SNAT, but this happens to work with one IP address (output address same as VIP address).

 

Is there something like "double" SNAT or any other method I could accomplish this on F5 LoadBalancer?

 

To sum up: I need outgoing traffic to has other IP address then snat address...

 

Any help will be appreciated.

 

Kind regards, Janusz