What an SOA record is
SOA stands for "start of authority". Every DNS zone has exactly one. It names the primary server for the zone and holds the numbers that secondary servers and resolvers use to decide when to refresh.
example.com. 3600 IN SOA ns1.example.com. hostmaster.example.com. (
2026101201 ; serial
7200 ; refresh
3600 ; retry
1209600 ; expire
300 ) ; minimumEach field in the result
| Field | Meaning |
|---|---|
| Primary server | The name server that holds the master copy of the zone. |
| Contact | The admin's email address with the @ written as a dot. hostmaster.example.com means [email protected]. |
| Serial | A version number. It must go up on every change, or secondary servers will not copy the new zone. Often a date plus a counter, such as 2026101201. |
| Refresh | How often, in seconds, a secondary asks the primary if the serial changed. |
| Retry | How long a secondary waits before asking again after a failed refresh. |
| Expire | How long a secondary keeps answering when it cannot reach the primary at all. |
| Minimum | How long resolvers remember that a name does not exist. |
Why the last number matters
The "minimum" field controls negative caching. Suppose it is 3600 and someone visits new.example.com one minute before you create that record. Their resolver remembers "no such name" for an hour, and the new subdomain looks broken for them until then.
A value between 300 and 3600 is common. Managed DNS providers set the SOA for you, and most do not let you change it.