What are hosted filters (Microsoft, Google, etc.)?

Hosted filters are cloud-based spam filtering services operated by mailbox providers. When you use Gmail, Microsoft 365, Yahoo Mail, or similar services, spam filtering is included automatically.

Google filters billions of messages daily across Gmail and Google Workspace. Microsoft provides Exchange Online Protection (EOP) for Microsoft 365 customers. These hosted solutions leverage massive scale to detect threats quickly.

The advantage of hosted filters is that they learn from aggregate data across millions of users. When a new spam campaign targets one user, the filter can protect everyone else within minutes. They also require no infrastructure from the customer.

For senders, hosted filters represent the majority of consumer and business inboxes. Understanding how Gmail and Microsoft filter is essential for deliverability.

Hosted filters are the shared harbor patrol, protecting an entire fleet rather than just one vessel.