The option notify determines whether or not our name servers send notify messages to any slave name servers, as determined by the NS records you have added in your domain.
Possible values for notify are:
yes no explicit
The default value of 'yes' means that notify messages are sent to all name servers defined in the NS records you have for the zone, with the exception of the name server specified in the Start of Authority (SOA) record.
A value of 'no' means you are not using any secondary name servers (i.e. only our name servers are handling DNS traffic for your domain).
A value of 'explicit' means that you will specify, via the 'also-notify' parameter, a list of IP addresses that are to be notified when zone changes occur, in addition to those name servers listed in the NS records of your domain.
Leaving the value blank inherits the global settings we use, which is the same as a value of 'no'.