Best Cloud based anti spam service

A cloud based anti-spam service is a “Software-as-a-Service” application that delivers high levels of spam and malware detection without capital outlay or high maintenance overheads. Implementation and configuration of the application is quick and easy, while the software and spam-detecting blacklists are kept up-to-date by the service provider.
Being cloud based, the service is compatible with every type of operating system and universally scalable – with no limit to the number of users that can connect to it. Consequently, a cloud based anti-spam service is an ideal solution for businesses of all sizes that want to reduce the volume of spam email they receive, increase productivity, and mitigate the risk from email-borne threats.

SpamStopsHere is hassle-free antispam that also provides zero-day email-borne antivirus protection. Very critical these days with email being a primary delivery mechanism for Cryptolocker and other dangerous malware. Unlike almost all of the alternatives out there, it does not rely on unpredictable Bayesian heuristics, so it blocks spam with almost no false positives. And chances are you won't have to do any filtering. Our analysts block threats 24/7/365 for our customers, updating our filters every two minutes.
Many IT departments and small businesses could never provide that level of protection on their own. Although we provide blacklists, whitelists and custom filtering, most customers don't use them and don't do any tuning on their own. It works really well.