What type of threats are commonly blocked by SEG attachment filtering?

SEG attachment filtering primarily targets known threats such as viruses and malware to protect users from malicious content. This is critical because these threats can be distributed via email attachments and can lead to significant security breaches if opened. The ability of the Secure Email Gateway to recognize and block attachments that contain harmful code is crucial in maintaining an organization's security posture.

The filtering mechanism often utilizes signatures, heuristics, and behavior analysis to detect such threats, ensuring that the end users remain safe from infections and data breaches that could arise from these attachments. This proactive approach allows organizations to mitigate the risk of malware propagation and potential data loss or system compromise.

Other options, such as marketing emails or spam messages, do not focus specifically on the threats associated with attachments, while blocking attachments based on size pertains more to storage and resource management rather than security threats. Hence, the focus on known threats makes this option the most relevant in the context of what SEG attachment filtering is designed to manage.