[exim4] rewrite left hand of email on outgoing mail

[Harry Putnam <reader@newsguy.com>]

Just now ran thru the ncurses interface you get with dpkg-reconfigure
exim4.config

On question you are asked is if you want to put a different domain on
outgoing email.... I chose yes and inserted `newsguy.com'

I never saw a way to rewrite the lefthand side of outgoing email.

I need it to be `reader' instead of my UID (harry).

That is, my outgoing `From: ' line and `envelope' info needs to say:

reader@newsguy.com  and so then the return-path will have the right
address.

I'm on a small home lan with single user on my localhost. I have a
fictitious domain `local.lan' so, `harry@2xd.local.lan' will be
meaningless on outgoing mail.  And, of course, will fail if anyone tried
to respond to `From: ' line.

So, where is that done in exim config?  (The domain part of the
rewrite is apparently handled during dpkg-reconfigure exim.config)

Here is the ncurses screen that handles the domain name change:

─────────────────────┤ Mail Server configuration ├──────────────────┐
The option to hide the local mail name in outgoing mail was enabled.│
it is therefore necessary to specify the domain name this system    │
should use for the domain part of local users' sender addresses.    │
                                                                    │
Visible domain name for local users:                                │
                                                                    │
newsguy.com_________________________________________________________│
                                                                    │
                   <Ok>                        <Cancel>             │
                                                                    │
────────────────────────────────────────────────────────────────────┘

Contents of /etc/exim4/update-exim4.conf.conf:

dc_eximconfig_configtype='smarthost'
dc_other_hostnames='2xd.local.lan;local.lan'
dc_local_interfaces='127.0.0.1 ; ::1'
 
  (**** this line below should handle the domain rewrite
  but what about the uid being rewritten?)

dc_readhost='newsguy.com'

dc_relay_domains='' 
dc_minimaldns='false'
dc_relay_nets='10.0.0.0/24;192.168.2.0/24'

   (smarthost munged)

dc_smarthost='xxxx.xxxxxxx.xxx:587'

CFILEMODE='644'
dc_use_split_config='false'
dc_hide_mailname='true'
dc_mailname_in_oh='true'
dc_localdelivery='mail_spool'