[Pkg-exim4-users] mailname for outgoing mail

[Ross Boylan]

I have a system with FQDN of corn.betterworld.us.
I want mail (also news posts and anything else heading to the internet
at large) from there to appear to be from betterworld.us.
I set /etc/mailname to betterworld.us.

Is that OK?  I guess that's a 2 part question: will it work?  is it
advisable?

Details and confusions:

I know the meaning if /etc/mailname and Debian policy on it has been a
sore spot (e.g., http://wiki.debian.org/EtcMailName).

The README.Debian discussion is a bit unclear to me:

   Your ``mail name'' is the hostname portion of the address to be shown
   outgoing news and mail messages (following the username and @ sign).
   What you enter here will end up in /etc/mailname, which is a file that
   might be used by other programs as well.
(exim4-config 4.61-1).

The "to be shown on outgoing" indicates betterworld.us is what I
want.  However, the documentation also refers to header rewriting
(actually, the very next paragraph says you may be able to hide this
name)--why would I want to hide it if it's the one I want to show?

I'm also unsure whether "hostname" in the previous discussion refers
to "corn" (which is what the command hostname returns) or to my FQDN.

Basically the same ambiguity occurs if I consult my current testing
man page for mailname:

  The file /etc/mailname is a plain ASCII configuration file, which on a
  Debian system contains the visible mail name of the system.  It is
  used by many different programs, usually programs that wish to send or
  relay mail, and need to know the name of the system.

  The file contains only one line describing the fully qualified
  domain name that the program wishing to get the mail name should use
  (that is, everything after the @).

I want the visible name to be "betterworld.us", but the FQDN of the
system is "corn.betterworld.us."

Corrently my setup is 
dc_eximconfig_configtype='smarthost'
dc_other_hostnames='corn'
dc_local_interfaces='127.0.0.1'
dc_readhost=''
dc_relay_domains=''
dc_minimaldns='false'
dc_relay_nets=''
dc_smarthost='x.y.com'
CFILEMODE='644'
dc_use_split_config='false'
dc_hide_mailname='false'
dc_mailname_in_oh='true'

Most (all?) the email on this system ends up forwarded to another one,
which is fine for now.  It may be I'm only getting away with my
current /etc/mailname because this unusualy behavior is what I need
now.  However, I'm about to put the system into use as my primary system,
including handling mail for betterworld.us, so I'm going to need to
change things.  I will be using split config.

P.S.  "The domain in a mail address need not correspond to a
hostname."  p. 24 of Hazel's Exim (3) book.  This suggests to me that
the use of "hostname" in the discussion of mailname may not be
entirely apt.  I also have a dim recollection that in some contexts,
in the edress user at a.b.com a is the "host" and "b.com" is the
"domain."