how can I rewrite the Mail From

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how can I rewrite the Mail From
\ ram (21 Jul 2007)

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Subject:	how can I rewrite the Mail From
Group:	Postfix-users
From:	ram
Date:	21 Jul 2007

Can I rewrite the mail from to implement SRS.

My mail server has been doing a lot of forwards and I see a lot of these
mails get rejected or tagged as spam due to SPF_FAIL

I use postfix 2.3.4 with cyrus

Thanks
Ram