Confirm that the SOA serial number of the zone corresponds to the most recent value.
# dig @server-IP-address SOA zone-name
[ENTER]
; <<>> DiG 9.3.0 <<>>
... ... ;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 1,
ADDITIONAL: 0 ... ;; ANSWER SECTION zone-name 3600 IN SOA servername
contact ( 2005092101 ; This should be the most recent value. ; This
value will most likely be different in your zone file. ... )
...