There are many different types of spam filters available, but most fall into one of two categories: blacklists and whitelists. Blacklists look at the content of emails and compare them against a list of known spammers, and Whitelists check email addresses and domains against a list of known safe senders.

Rule-Based Filters – Rule-based filters are great for those who want to stop spam. You set up rules that match certain words or phrases in an email. Then you can tell your mail client to forward messages that contain these words or phrases to a spam folder.

Blocklist Filters – A blocklist filter blocks spam emails from senders added to a complete spammers list. A blocklist filter is updated regularly to keep up with spammers who change their email addresses. Enterprises often create their blocklists to protect their business interests, such as blocking headhunters seeking their top talent for the benefit of other companies. Enterprises can also block emails deemed wasteful of their employees’ time.

More info: What is the Border Gateway Protocol (BGP)?