Spam is something that all internet users encounter almost every day. The two basic kinds of spams are email spams and virus spams. Email spams work by checking websites for the @ symbol, which helps identify email addresses. Virus spamming refers to infecting a computer with a virus that would pick up email addresses from address books for targeting with spam emails. Spam filters are either signature-based or rule-based, located on central servers or on local computers.”]
Source: https://hackercombat.com/what-is-spam-filter-and-types-of-spam-filters/