Reverse DNS not working

[Shayne]

Hiya

I am picking up certain mails are not coming through because of HELO or DNS Mx setting problems. A little research and I think its because of the dns on my box.

When I type host test.mydomain.com I get the following a good response but when I type the host 11.11.11.11 then I get:
not found: 3(NXDOMAIN)

What steps must I check or how do I setup the dns correctly.

Just as a point of interest I am new to dns.. and the test.mydomian.com is not regitered anywhere its just a domain I thought up for this box which has a fixed IP.

Regards