def emails_are_valid?(emails)
     regex = /^(\s*[a-zA-Z0-9\._%-]+@[a-zA-Z0-9\.-]+\.[a-zA-Z]{2,4}\s*([,]{1}[\s]*[a-zA-Z0-9\._%-]+@[a-zA-Z0-9\.-]+\.[a-zA-Z]{2,4}\s*)*)$"/
     !!emails.match(regex)
end

p emails_are_valid?("mm@somedomain.com aa, mma@somedomain.com")

false