I have test mail server Zimbra 7.0 on Linux Suse 11

when I telnet.

- telnet 110 - OK Zimbra POP3 server ready
- telnet 25 - 220 ESMTP Postfix ??

Is this status OK for port 25 ????

I can send messages to gmail, hotmail, ...
I can NOT send messagest to mail domain @example.si ??
Log say:
- Host or domain name not found. Name service error for name=example.si type=A: Host not found

What I have to fix in zimbra for this Error