configuring sendmail to accept verification for other server

We have a remote, off-site (redundant, sorry) production server our domain name points to. Let's call it "X.domainname.com".

We have a small web server at the office that performs a couple but vital functions that needs to send an e-mail out about twice a day to two different external recipients. It has no domain name pointed to it.

Every email that goes out from the local server, let's call "Y.localdomain", that goes out gets returned with:

The original message was received at Mon, 24 Apr 2006 21:16:47 -0500 from localhost 127.0.0.1

----- The following addresses had permanent bane errors -----

----- Transcript of session follows ----- ... while talking to celticbear.com.:

Now, it works fine if I replace the Y server'setc-sysconfig-network 's HOSTNAME=Y.localdomain with HOSTNAME=X.domainname.com

Works perfectly. However, and there may be no way around this if this is the only way to get it to work, but a few of us SSH shell into the local server AND that remote server, and if the local HOSTNAME= matches the remote server's, the command prompt and shell window breastle bar are the same for both servers and that can cause no end of confusion and accidentally doing something on one server meant for the other.

I'd like to find some way in which the HOSTNAME= can be different and unique, but the mail from it still be accepted as verifyable. I can change the local domainname to the remote's domain name, and that makes the sending server in the mail headers become "Y.domainname.com" but the existance of that machine name "Y" prevents the verification.

So looking into SENDMAIL options I tried the "domain masquerading" but that didn't change a single thing in the header. I added the outgoing user to "trusted users" but also no difference.

I also added define(`confDOMAINNAME',`X.domainname.com') to the sendmail.mc to have it compiled into the .cf, which it did, but made no difference.

Thinking the problem is, or at least partly, the remote server only accepting verification checks from itself (X.domainname.com) and obviously not for Y.domainname.com, I looked into its SENDMAIL options. I added Y.domainname.com to "local domains" and "relay domains" but still no change.

I've reached the end of what I can find to try. Any other suggestions? Thanks!! =)