What’s the difference between server-side and client-side filters?

Server-side filters operate at the mailbox provider level, processing messages before they ever reach your inbox. Gmail, Outlook.com, and Yahoo Mail all run server-side filtering. These filters have access to global reputation data and can block spam at scale.

Client-side filters run locally in your email application, such as Microsoft Outlook desktop, Apple Mail, or Thunderbird. They process messages after download and can apply personal rules, but they lack the global intelligence that server-side systems possess.

Server-side filtering is where the heavy lifting happens. By the time a message reaches your client, it has already passed through multiple layers of server-side analysis. Client-side filters add a personal touch, letting users create custom rules for organizing or blocking specific senders.

Server-side filtering is the coast guard intercepting threats at sea. Client-side filtering is your personal dock security deciding which packages to accept.