RFC 1918 addresses

Exposing an RFC 1918 private address in, say, a "Received:" header in

e-mail

is less of a problem, though the spammers who do it are actually better

able

to cover their origins, there's no way to prevent it and no normal damage

from doing it.

Unless the SMTP server used to proxy email through a firewall is able to
strip headers, it's unavoidable.
I would like to see that feature added to SMTP servers, however, I do hate
letting internal host names and addresses out.

  Matt

I believe a number of firewall packages and a few anonymous remailers
(sendmail based) support header stripping. I know for a fact spammer
software does it.

-Deepak.