Email filtering uses a combination of techniques to assess the content, sender, and other attributes of incoming emails. These techniques include:
Blacklisting
Blacklists include a list of domains or IP addresses associated with malicious or unwanted senders. Emails from these senders are automatically blocked or filtered to prevent them from reaching the user's inbox.
Content filtering
Often, spear phishers will convince their victims that they have only hours—or even minutes—to send a wire transfer, change their bank account information, or purchase gift cards for clients.
Reputation-based filtering
This filtering method assigns a reputation score to emails based on factors such as IP addresses and past actions of the sender. Email filters typically block messages with low reputation scores and prevent them from reaching a user’s inbox.
Whitelisting
While blacklisting prevents users from receiving messages from a specific sender, whitelisting does the opposite. Emails from senders on the whitelist are always delivered regardless of the content of their messages.
Bayesian filtering
Bayesian filtering prevents spam from reaching a user’s inbox using a statistical model. This method of filtering evolves over time as the filter learns to distinguish between legitimate and spam messages.
Language filtering
Language filtering blocks emails written in a foreign language and prevents them from reaching a user’s inbox.
