You could automatically email a report to you via storagescope but you cannot enable that email based on criteria within the report, it's either on or off. That's not pretty but it may be the quickest way to let you keep an eye on it until you get something more sophisticated.

If you are by chance looking for the amount of storage left in a save pool then there are a couple of alerts right in control center for 90% full and 100% full. You can have that alert use a management policy that sends you an email. Very limited in flexibility but if it's save pools you're looking for you can at least set of some proactive alerting on it's usage.

More likely to get what you want you would need to do something like have a script periodically query storagescope via the API and then send an email based on its return. You'll need to carefully consider what stats you're examining as some people have different definitions of free space.

Where can I find that option of automatically sending an email of report through storagescope?

Protoss,

You can schedule a report, and in the process you have an option to send it to email. I am not sure whether we can email already generated reports, if that's what you are looking for.