Postfix/Exim sender address rewriting (was: Postfix ... ComCast port 587)

[Ben Scott]

On Tue, Jan 20, 2009 at 12:02 PM, Ben Scott <dragonhawk at gmail.com> wrote:
>  ... Sendmail ... /etc/mail/genericstable:
>        bscott  dragonhawk at gmail.com
>
>  I presume Postfix has a similar capability.  Exim may as well.  Anyone?

  I'm disappointined nobody has posted an answer to the above.  I'm
changing the subject line and reposting to try and call attention.
This seems like a real useful thing to know how to do.  For me, for
others reading, for the list archives.

  The goal here is to configure one's MTA (Mail Transfer Agent) such
that mail from a local-only email address gets rewritten to an valid
public Internet email address.  For example, on my home PCs, my *nix
username is <bscott>.  If I send mail from a local program, the
sending email address generally becomes something like
<bscott at blackfire.bscott.local>.  That's obviously not going to be
useful on the Internet.  So I have configure my MTA (which happens to
be Sendmail) to re-write those to be <dragonhawk at gmail.com>, which is
my public address.

  How does one do this in Postfix and/or Exim?

-- Ben