Recommended SOA values

STRUCTURE OF A SOA RECORD

domain-name TTL SOA MNAME RNAME (SERIAL-NUMBER REFRESH RETRY EXPIRE MINIMUM-TTL )

RECOMMENDED VALUES

example.com.  3600  SOA  dns.example.com. hostmaster.example.com. (
                         1999022301   ; serial YYYYMMDDnn
                         86400        ; refresh (  24 hours)
                         7200         ; retry   (   2 hours)
                         3600000      ; expire  (1000 hours)
                         172800 )     ; minimum (   2 days)

REMARKS AND EXPLANATION

MNAME
the primary master DNS server

RNAME
public mail address of a person or a role account deling with DNS zone
The "@" need to be converted to "." , so hostmaster@mydomain.com need to be reported as hostmaster.mydomain.com
RFC2142 suggests to use a dedicated mail alias "hostmaster", but it's not mandatory

SERIAL NUMBER
In the  YYYYMMDDnn scheme and must be replaced by proper values for 
the year (YYYY, four digits), 
month (MM, two digits), 
day of month (DD, two digits) 
and version per day (nn, two digits). The first version of the day should have the value "01". 
It is important to preserve the order year - month - day.

REFRESH VALUE
The time (in seconds) until a slave DNS server needs to refresh his recorded DNS data
suggested value: 86400 (24 hours) 

RETRY VALUE
suggested value: 7200 (2 hours)

EXPIRE VALUE
The time (in seconds) a data recorded is valid, even if an outage put off primary DNS server
suggested value: 3600000 (1000 hours)

MINIMUM TTL
suggested value: between 3600 and 172800 (1 to 48 hours)