Date:        Wed, 11 Jul 2001 02:01:33 -0400
    From:        "James K. Lowden" <jklowden@lowden.schemamania.org>
    Message-ID:  <20010711020133.A11809@lowden.schemamania.org>

  | It's running an unmodified sendmail (uses the default configuration), so 
  | mail from mutt  carries a "from" address of 
  | jklowden@lowden.schemamania.org.  You can't send mail there because 
  | it's a non-routed ip address behind a NAT firewall.

I don't know mutt at all, but this might be something mutt is doing,
in which case it would need to be adjusted there.   If mutt isn't adding
the From: headers (it probably should be, they're an MUA issue, not MTA)
then sendmail will be, and to do:
 
  | I want to "rewrite" (I think) the from address to 
  | read: jklowden@schemamania.org.

you want to use the MASQUERADE facility in the sendmail.cf (via the
m4 files).   Look in /usr/share/sendmail at the README file, then in the
cf sub-directory, build your own config file template (starting from the
NetBSD example).

  | In a related question, I do receive mail @schemamania.org (on a host 
  | called "home"), but that sendmail plunks the mail into its local spool 
  | instead of forwarding it to "lowden".  I get around this with a .forward
  | file, but I'd like to know what the right way is.

For most people, .forward is the right way.   It is certainly an adequate
way assuming that all users have accounts on the mail hub (if not, there's
the user database you could define, but I'd just stick with .forward, or
the aliases file).

  | Do I really have to learn m4 and build a half dozen files to do this?

For the first part, you have to build one file, which will result in
another being built when you run m4.   About all you need to know about m4
to do this is how to type "m4" (or more often, "make") - and how to use
your editor - you will be using pre-defined m4 macros, not attempting to
create your own.

kre