I like that it has multiple modes of protection for different types or emails (incoming/outgoing).
It also helps block spam messages from reaching your inbox in real time which is very helpful when you're working online all day long! Nothing really at this point but they are constantly updating their service so i'm sure there will be more features added as well soon enough :) If used correctly then mail guard can help keep incoming junk mails away while still allowing needed information through without being blocked by filters set up elsewhere such as gmail's filter etc..