What Does the Mail Gateway Do?

About this interactive

A mail gateway protects the front end of the mail system: ideally it is the first MTA that inbound mail reaches. It runs a series of checks, and every product orders and scores them a little differently. First come the lists. A sender on the deny list is refused. A sender on the allow list is expedited and skips the other checks. Everything else goes through checks such as SPF, DKIM, DMARC, anti-malware and spam lists, which may be kept by a third party you pay or by open sources. Rather than refuse a message for one failure, the gateway gives it strikes. That is how a softfail works: it is not a refusal, just points against the message. At the end the total decides the outcome: delivered (perhaps labelled as spam), quarantined until the user releases it, or rejected. The point values in this set are this gateway's. Real products use their own scores and limits.

What you'll learn

Predict whether a mail gateway delivers, quarantines or rejects a message from its deny and allow lists and the strikes it adds up
Explain why a mail gateway sits at the front of the mail system and how a softfail counts as a strike rather than a refusal

Aligned to

CompTIA Security+

4.5 Given a scenario, modify enterprise capabilities to enhance security.

Key terms

Mail Gateway: A security checkpoint positioned at the front of a mail system that filters inbound email through a series of checks, including allow/deny lists, authentication protocols, and anti-spam mechanisms, before passing messages to internal mail servers.
Quarantine: A disposition action taken by a mail gateway that isolates suspicious or high-scoring email messages for review rather than delivering them directly to the recipient or dropping them outright.
Spam: Spam is unsolicited bulk electronic messages, most commonly email, that serve as a primary delivery vector for phishing campaigns, malware attachments, and social engineering attacks.
Allow List: An application control approach that permits only explicitly approved applications to run, blocking everything else by default.
Deny List: An application control approach that blocks only explicitly named applications, permitting all others to run by default.

Topics

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