I was getting hundreds of spams a day, and having a client based filter wasn't cutting it, because I am always using webmail. This service will act as the middleman and delete the spam before it gets to your inbox (Webmail, or Desktop) this includes most viruses.
To top it off the service is free for life, and as low as $25 a year for preimum support. I was desperatley looking for a service like this, and only 2 came up, this one or another that was 10 bucks a months and not as loaded.
As a premium user you get a 50MB IMAP/POP/SMTP server access, and unlimited email accounts.
Best of Luck, if you do try Premium (I paid for 2 years the day I looked at the site) you get 30 days to decide if it is for you or not.