Recommended pre-queue setup for Postfix

[Cristian Seres]

Hello,

I would like to get an opinion which is the best configuration for 
incoming only Postfix mail gateway that should
  - Reject virus, banned destiny and clear spam messages during SMTP 
session. It is important for us not to send backscatter to forged sender 
addresses. This implies using pre-queue setup for Amavis, right?
  - Work in co-operation with opendkim-milter i.e. not break DKIM 
signature - or configure amavisd-new to check DKIM with option to 
discard email if sender domain's DKIM ADSP policy suggests to do so.

Is the best practice in this case to use smtpd_proxy_filter setting in 
Postfix's main.cf and what are recommended settings to master.cf and 
amavisd.conf to go with it? Or is there some better way to do it nowadays?

Amavisd-2.7.0, Postfix 2.6.6. About performance requirements: less than 
15k incoming email per month which will be divided to two or three MX 
servers.

I am looking forward to your suggestions.

-- 
Cristian Seres