Up Down Alert not working . But test mail is working

[racac]

Hi

i have configured cacti 8.8b Graph is looks good.and enabled threshold and manage monitor pluggings installed . i am able to get test mail through my SMTP . but i could not get Host Up and DOwn alerts .

i have enabled the UP and down alerts only one time i received Up alerts . then i did not rececived any alerts.

can anyone please help us exact guide to enable Alerts

Please confirm if i missing anything here