I´m at an Oracle Enterprise Server 5, and I trying to configure the sendmail service for some Oracle applications can send e-mails. I've been configuring the sendmail and bind service, the sendmail is ok but the bind I´m not sure. I put a domain.hosts configuration at named directory and configured my LAN DNS at resolv.conf, I try to ping my local mx address, mx.domain.com but it returns unknown host....
I´m a little lost and it´s first time I configure something like this anybody already configure this before...

PS: It´s a test server inside a LAN if proxy authentication and it only needs to have the sendmail configured to act as simple smtp server for the localhost....

You don't need to run bind just to do this. Add entries to /etc/hosts and it'll pick them up from there within sendmail, which again you should have no need at all to modify from the default installation settings.

Do you mean put like this:

10.216.x.x ns.domain.com ms.domain.com

???

I think configured sendmail right because I can send messeges directly to the to computer users and when I put # nmap localhost, I notice that my port 25 is open but I still can´t send e-mail outside. Do I need or not to have a DNS server configured?

well naturally there is a need for name resolution, but for internal deliveries, you'd only need to be able to resolve the domain part of an email address to an IP, and for internet addresses, merely having a functioning external DNS server listed is fine.