sendmail not working

Good afternoon,
I have been trying to setup sendmail to work with PHP, but cannot seem to get it working correctly.

What Im trying to do is configure sendmail to relay all emails through another SMTP server on my network, I have downloaded and installed sendmail correctly (I belive), and configured it to send mail through my SMTP server, however when I try and do the command at the terminal "sendmail test@mydomain.com" I get no error, but in my mailbox (on the server) I get:-

The original message was received at Tue, 17 May 2011 15:33:37 +0100
from localhost [127.0.0.1]

   ----- The following addresses had permanent fatal errors -----
<email@tonycross.me.uk>
    (reason: 550 Host unknown)

   ----- Transcript of session follows -----
550 5.1.2 <email@tonycross.me.uk>... Host unknown (Name server: 192.168.2.25: host
not found)

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If I try and telnet to 192.168.2.25 on port 25 from the server, everything responds correctly.

What Im trying to do is get sendmail working at the command line at first, then fugure out why my php.ini doesnt work.

Im not really sure what I can upload to get any help with this, obviously its my onfiguration thats the issue, but not sure where the configuration file is to email you.

Any help would be appriciated.

Thank you