Hi,

In this guide: Ubuntu 8.04 LTS Server (Hardy Heron) Install Guide - Zimbra :: Wiki

In the section of DNS server what does it mean "host id":

"..."
Now create your file /etc/bind/db.xxx.xxx.xxx

$TTL 3D
@ IN SOA mail.mydomanin.com. admin.mydomain.com. (
1 ; Serial
8H ; Refresh
2H ; Retry
4W ; Expire
1D) ; Minimum TTL
NS mail.mydomain.com.
x PTR localhost.

Where "x" indicates the host id.
"..."

Thanks in advance

Regards,
Rafael