My server has 2 ips: x.x.x.73 and x.x.x.248. I can access my site via these ips, 
using Web browser.
{Now, from a CentOS machine (not my server), using terminal} 
If I:
dig @x.x.x.73 mydomain.com 
dig @x.x.x.248 mydomain.com
I get the result:
Connection timed out; no server could be reached.
Could somebody please tell me how to fix it? Thank you.
More information:
If I log in to my server using ssh and do:
dig @x.x.x.73 mydomain.com
dig @x.x.x.248 mydomain.com
I can see my zone shown as expected:
; <<>> DiG 9.3.6-P1-RedHat-9.3.6-16.P1.el5_7.1 <<>> @x.x.x.73 mydomain.com
 ; (1 server found)
 ;; global options: printcmd
 ;; Got answer:
 ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 12757
 ;; flags: qr aa rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 2, ADDITIONAL: 2
 ;; QUESTION SECTION:
 ;mydomain.com. IN A
 ;; ANSWER SECTION:
 mydomain.com. 38400 IN A x.x.x.73
 mydomain.com. 38400 IN A x.x.x.248
 ;; AUTHORITY SECTION:
 mydomain.com. 38400 IN NS ns2.mydomain.com.
 mydomain.com. 38400 IN NS ns1.mydomain.com.
 ;; ADDITIONAL SECTION:
 ns1.mydomain.com. 38400 IN A x.x.x.73
 ns2.mydomain.com. 38400 IN A x.x.x.248
 ;; Query time: 20 msec
 ;; SERVER: x.x.x.73#53(x.x.x.73)
 ;; WHEN: Sun Jan 15 11:46:30 2012
 ;; MSG SIZE rcvd: 129
BIND version 9.3.6, Centos 5.
Logging to my server using ssh, do inga "dig google.com"
also shows expected  results.