Best place to filter spam (x-original-to, no_address_mappings)

[MRob]

Hello,

I posted this question to the Postfix list and it occurred to me that 
the SA community could be just as (or more) informative:

I am looking at a system where SpamAssassin is called out from the 
delivery agent. I know there will be a difference here in terms of the 
envelope information but I'm not familiar enough to know the pitfalls of 
this versus calling SA from the postfix content_filter.

Specifically, I believe it's recommended to call SA in context of 
receive_override_options=no_address_mappings but this wouldn't be the 
case when we are in the delivery agent I think. What are the effects of 
this?

Also, if it's possible to have LMTP send the original envelope sender 
(x-original-to?), would that help? And is that possible yet in the 
newest version of Postfix?