Guys, we have to make it clear that this will not prevent a SPAM email from arriving in the user's email inbox.
To do this, you need an anti-spam solution (which also does not guarantee this 100%).
The solution that Meraki offers is limited to filtering what you access via the WEB.
I am not a Cisco Meraki employee. My suggestions are based on documentation of Meraki best practices and day-to-day experience.
Please, if this post was useful, leave your kudos and mark it as solved.