The correct answer is Email processor.

The Email processor is the component that inspects inbound messages and runs spam detection and classification logic, so it marks messages as spam. In a mail pipeline the processor is responsible for analyzing message content, applying rules or models, and annotating or flagging messages for downstream handling.

The Email processor typically updates message headers or metadata to indicate spam and then allows the routing or delivery components to act on that classification. This separation keeps fetching and transport duties distinct from content analysis and makes it clear that marking for spam belongs to the processor.

Mail handler is usually a routing or delivery component and it does not perform the content analysis needed to mark spam, so it is not the right choice.

Cloud Pub/Sub is a messaging transport that moves events between services and it does not analyze or classify message content, so it would not mark messages as spam.

Email fetcher retrieves inbound messages from external servers and focuses on collection rather than inspection, so it would not be responsible for marking spam.

Email puller is similar to a fetcher and its role is to pull messages into the pipeline rather than to perform classification, so it would not mark spam.

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