This functionality is somewhat provided by default through the periodic system.
... to /etc/periodic.conf and you'll be all set. However, all this does is sent you a daily status report for your ZFS pools. I'd assume you could simply use some mail client filter rules to check for anything matching degraded.
Another option is to write such a script yourself: zpool status | grep -i degraded should be enough. If you run that through crontab then it will only produce output whenever a pool is degraded, and cron only sends e-mails when commands produce any output.