Question: Explain why features built from a message's envelope or header information can help a mail filter detect spam. In what way does this routing information give a useful signal that is different from the message text?

Sample answer: A filter can use envelope and header fields to reconstruct the path a message took through mail servers before it arrived. This is useful because large spam campaigns often reuse the same relays, hosting providers, or delivery patterns. Features based on those routes let the system flag messages tied to suspicious infrastructure, even when the wording of the email is changed or looks harmless. That makes routing data a complementary signal to content analysis.

Key points:

• Notes that headers and envelope data can reveal the servers a message passed through.
• Explains that spam is often sent through repeatable or suspicious infrastructure.
• Distinguishes infrastructure-based evidence from evidence based on the email body.

Rubric: The essay must explain that envelope/header data can be used to trace delivery paths and that this path-based information can help identify spam independently of message content.