Amavis and Postfix in a cluster with smtpd_proxy_filter

[Carsten]

Hello all together,

I've got a question to my clustering setup.

I've got several firewalls, which receive Mails from the Internet, and 
they should send them to dedicated amavis nodes for scanning.
This should be done by using smtpd_proxy_filter to be able, to directly 
reject spam and virus messages.

The Firewalls have the IPs 10.1.1.1, 10.1.1.2 and 10.1.1.3
I have got a loadbalancer VIP 10.2.2.1:10024, which sends the packets to 
the dedicated amavis nodes 10.2.2.5:10024 and 10.2.2.6:10024.
The problem is the way back to one of the firewalls. I know, that I can 
use $forward_method and $notify_method, but which IPs should I put in there?
I don't know, which Firewall is sending the request to amavis at the 
moment, so i can't statically define the IP to send back on Port 10025.
I think, the mail needs to go back to the same Firewall von Port 10025, 
which originally contacted amavis.

How can I archieve this or is there a better way to use amavis in a 
cluster setup?

Thanks in advance

Carsten