Mail Server Accused of Spam!

[Tim Smith]

Hello,

I have a few users who just want their email forwarded onto GMail 
Accounts however these users seem to receive an inordinate amount of 
spam and so I get a message from Google in my logs stating:

/Feb  7 09:39:53 xxxxxxx postfix/smtp[15191]: 118C8C0C2A6: host 
gmail-smtp-in.l.google.com[173.194.78.26] said: 421-4.7.0 
[xx.xx.xx.xx      15] Our system has detected an unusual rate of 
421-4.7.0 unsolicited mail originating from your IP address. To protect 
our 421-4.7.0 users from spam, mail sent from your IP address has been 
temporarily 421-4.7.0 rate limited. Please visit 
http://www.google.com/mail/help/bulk_mail. 421 4.7.0 html to review our 
Bulk Email Senders Guidelines. fk8si1147119wib.80 - gsmtp (in reply to 
end of DATA command)/

That's fine and I totally understand why they do that but is there a way 
that Postfix can flag the message so that Google understands that we are 
just forwarding the message and that we are not the originator of the spam?

Cheers,

Tim