Secure email gateway
A secure email gateway (SEG) inspects email passing through a mail delivery path and applies policies to block, hold, or otherwise handle unwanted or dangerous messages.
A control in the mail delivery path
The gateway examines mail according to the protections and policies enabled for it. Checks can include sender reputation, message content, links, and attachments. Depending on the result, a message may be rejected, delivered, or placed in quarantine.
Cisco’s gateway documentation also describes outbound data-loss policies and deployment in cloud, on-premises, or hybrid environments. The name does not require a physical appliance in the office. Microsoft documents a related filtering pipeline built into its cloud mailbox service. Confirm the actual mail route before deciding which product inspected a particular message.
Passing a filter is not approval of a request
A message reaching the inbox does not establish that its invoice, password-reset request, or claimed sender is legitimate. Filtering and business verification answer different questions.
When investigating a message, start with the gateway’s recorded action: did it reject, deliver, or quarantine it? Then follow any later activity in the mailbox or on the device. The SOC visibility article explains which parts of that sequence different tools can show.
For messages held at the gateway, the quarantine release guide covers release and sender-allow decisions.