you can do it by defining Breach Duration.
If you have a poller time of 1 minute and you need to send email after a while a threshold was breached, you have to define a breach duration longer than poller time.
Poller Time: 1 Minute
Breach Duration: 5 Minutes
With this settings you get an email each 5 Minutes and oly if threshold was breached more than 4 times (if you have a poller time of 1 Minute).
If you want to reduce realert, simple clic on Re-Alert Clic and choose a different period of time.
I hope i have understood your problem and clarified it.