What to put into the SOA DNS entry field?

Here is an example zone file for a domain that also hosts its own name server. The primary name server and mail server are on the same IP as the domain. Another machine hosts the secondary name server and the backup mail server. This other machine must be configured for both tasks, and you need glue records at the registrar.

$ttl 10800
example.com.    IN  SOA ns1.example.com. root.example.com. (
            1239719044
            3600
            3600
            604800
            38400 )
example.com.    IN  NS  ns1.example.com.
example.com.    IN  NS  ns2.example.com.
example.com.    IN  A   123.123.123.123
example.com.    IN  MX  0 mail.example.com.
example.com.    IN  MX  10 mail2.example.com.
example.com.    IN  TXT "v=spf1 a mx ptr ?all"
ns1.example.com.    IN  A   123.123.123.123
ns2.example.com.    IN  A   234.234.234.234
localhost.example.com.  IN  A   127.0.0.1
mail.example.com.   IN  A   123.123.123.123
mail2.example.com.  IN  A   234.234.234.234