masquerading domain name

Gawd, sendmail is so above my understanding. We have a local Linux fileserver that has to send mail out. But it doesn't have an actual domain name, just an IP address. Our domain name is pointed to our remote server. So, in the fileserver in theetc-hosts file I had:

127.0.0.1 localhost localhost.localdomain localhost (local IP address) fileserve fileserve.(our domain name).com (remote IP address) (our domain name).com alpha

With that, mail sends fine in general, except to a couple of specific recipients that refuses the main because: rejected: Domain not found

So I tried to change theetc-hosts to:

127.0.0.1 localhost localhost.localdomain localhost (local IP address) fileserve (our domain name).com (remote IP address) (our domain name).com alpha

but then that simple change would no longer send mail out to anyone. So I changed it back, and the focus is going to have to be making the e-mails come out as from the remote server that has the domain name pointed to it.

How in the world??! Just a clue like "look into this file-concept-Webmin tool for Sendmail" and I'll try to figure it out.

(I use Webmin to manage Sendmail, because I looked into using M4 and whatnot, and oh my god! I am WAY too dense to manage Sendmail without a GUI!)

Thanks for any suggestions or advice! -Liam