Inbound mail filter (email gateway): what it is and how it is attacked
The thing that inspects email on the way in and decides what reaches somebody's inbox.
Also known as
- email gateway
- secure email gateway
- SEG
- Mimecast
- Proofpoint
- spam filter
- mail security
Typing any of them into the editor finds this object.
Why it matters on a security diagram
Every phishing write-up has to say whether the message passed a filter or whether there was no filter in the way. Drawing it forces that question to be answered rather than assumed.
How it gets attacked, and what reduces it
How it gets attacked
- A message that carries no attachment and no link, which most filters have nothing to test
- A link that is harmless when scanned and changed after delivery
- A thread that arrives from a real supplier's real mailbox, which is not a forgery at all
What reduces it
- Check alignment as well as the sending record, so a message that merely passes a check is not treated as verified
- Rewrite links and check them at the moment somebody clicks, not only on arrival
- Accept that a genuine account sending genuine mail defeats this layer entirely, and put the second control on the payment rather than the message
Where it sits
- Group
- Security and edge · The things that sit in front of something else and check what is trying to reach it.
- Whose side, by default
- Ours · Belongs to the organisation the diagram is about.
- Catalogue identifier
- mail-gateway
Reviewed . CC BY 4.0.
Others in security and edge
- FirewallNGFW · packet filterDecides which connections are allowed between two networks.
- Web app shieldWAF · web application firewallChecks visits to your website and blocks the ones that look like an attack.
- Outbound web filterforward proxy · secure web gateway · SWG · web filter · web proxyChecks and records everything staff and servers send out to the internet.
- Traffic splitterload balancer · LB · ADCSpreads incoming requests across several servers.
- Global content cacheCDN · content delivery network · edge cacheCopies your content to servers worldwide so pages load faster.
- API front doorAPI gatewayOne controlled entrance for the automatic requests other software makes of yours, without a person involved.
- Endpoint protectionEDR · antivirus · AV · XDRSoftware on each computer watching for hostile behaviour.
- Log collectorSIEM · log server · syslogCollects the records of what happened, from every computer and system, into one place.
- Secrets storevault · secrets manager · credential store · password safeThe safe where passwords, keys and certificates are kept.
- Encryption key serviceKMS · key management service · key vault · HSM · customer-managed keyThe service that holds the keys used to scramble stored data, and decides who may use them.
- Cloud activity recordCloudTrail · activity log · control plane log · audit trailThe provider's own record of every change made to the cloud, and of who made it.
- Remote support toolRMM · remote monitoring and management · ScreenConnect · ConnectWise · AnyDesk · TeamViewer · Splashtop · remote support · screen sharing toolSoftware that lets somebody else take control of a machine over the internet, usually a support company.
- Network monitoring sensorIDS · IPS · NDR · intrusion detection · intrusion prevention · packet capture · network detection · SPAN · TAPSomething watching the traffic on a segment and recording or alerting on what it sees.
The security and edge group lists all 14 of them side by side.
Inbound mail filter on your own diagram
Open the editor, press N, and type email gateway. The object is placed and connected to whatever was selected, and Tab adds the next one already joined to it. Nothing is uploaded: the page is served with a Content Security Policy that forbids the browser from making any outbound request at all.
Open the diagram maker