A server spam filter is a type of spam filter that's actually integrated into your SMTP server so that spam is sieved and removed outright on the server level before it can even reach your inbox.
Many of these spam filters have a very simple and affordable implementation as well as industrial-grade spam filtering capabilities, which makes a lot of sense because they're best used by Internet service providers (ISP) and enterprises running their own online servers.
More often than not, end users have no use for this product because it's been specifically made to tackle corporate-level spam control, which means it handles spam by the millions daily instead of just the thousands or the hundred thousands.
A server spam filter gets all the emails addressed to your domain and employs several different filtering approaches simultaneously to detect spam-like attributes in messages even before they have a chance of landing in your inbox.
Only when the correspondences are verified to be legitimate can they be forwarded to your SMTP server.
Is also capable of becoming the spam filter gateway of your company's server, which means that it can easily eliminate spam at the server level without the need to update or install any run-of-the-mill anti-spam software on each and every last workstation of your office or department.
They also have handy features like easy installation, intuitive management, and all-inclusive protection via a comprehensive set of services such as the Bayesian statistical analysis service, advanced Bayesian pattern matching, and universal SMTP support.
As for the premium-grade server spam filters out there, their superiority usually stems from the large amount of services that are employed to detect server-level spam, which could include a distributed blacklist database that's updated real-time automatically, a sender policy framework (SPF) that verifies the validity of a sender's address, a centralized hash signature database.
Automatic whitelists, SURBL spam filter testing of email links, embedded image scanner, country-blocking capabilities, DomainKeys support, neural network sender matching technology, challenge response, URL DNS checking, Microsoft Exchange Integration for Windows-based machines, DNS-based block lists, DNS MX mail records configuration testing, optional anti-virus, and user-defined keyword blocking.