sendmail and "sender domain must exist" error

[Timothy Stone]

List gurus and sendmail magicans,

I'm running an installation of RHL 8 (psyche). Mainly an internal 
staging server for web development. While I'm not using it as a mail 
host I have left sendmail running for reasons that are novice at best, 
but worked until my employer, in a cost saving move, yanked everyones 
cell phones and replaced them with alpha pagers.

The pager host excepts email, but are very strict about excepting mail 
from domains that don't exist. While I applaud the pager host supporting 
SPF or someother anti-spam effort, it has hosed my cron job reporting 
that I relied on each morning to know that logging updates and other 
tasks completed.

So, I have tried to configure sendmail since the switch to work, but the 
problem is that the machine is behind a firewall and has no outside 
address.

The machine name is psyche.harrisburgpa.gov. Yes, I have internal DNS 
running but this DNS does not notify our host DNS, it acts only 
internally as a caching name server and for internal machine lookups 
(mainly used only by me as our lousy network admin doesn't care for DNS 
or is afraid of it or ... i don't know.)

So while our network provider has DNS records for things like www and 
the "harrisburgpa.gov" record is out there for querying, but "psyche" 
and "mail" are only known internally.

How do I fix this, either on sendmail, DNS, or use sendmail to forward 
to our real mail host? I'm sure it's documented somewhere, but I'm just 
not querying the right words or looking for the wrong thing.

Many thanks in advance,
Tim

Here's some logging to help:

...
The original message was received at Thu, 17 Jun 2004 07:03:15 -0400
from psyche [127.0.0.1]

    ----- The following addresses had permanent fatal errors -----
<717xxxxxxx at page.metrocall.com>
     (reason: 501 <analog at harrisburgpa.gov>... Sender domain must exist)

    ----- Transcript of session follows -----
... while talking to popserver4.metrocall.com.:
 >>> MAIL From:<analog at harrisburgpa.gov> SIZE=810
<<< 501 <analog at harrisburgpa.gov>... Sender domain must exist
501 5.6.0 Data format error
...


[analog at psyche analog]$ mail -v registrant at petmystone.com
Subject: test
test