how to remove received by headers before mail gateway

[Eero Volotinen]

I am running ssl+sasl authenticated mailgateway and problem is that in 
some cases clients from world are sending mail from "blacklisted" networks.

The main problem is that spamassasin is analyzing received headers and 
it might tag message as spam by received by headers.

So, How I can remove headers only from outgoing mail using:
http://www.posluns.com/guides/hedrem.html


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Eero