Sender reputation is a trust score email systems assign to a message source based on the sending domain, the address history, and prior abuse signals. Mail gateways use it to judge whether a message is likely legitimate, suspicious, or malicious before it reaches the inbox.
In cyber security, sender reputation matters because phishing campaigns often rely on disposable or newly created addresses that have little positive history. Defenders can combine reputation with URL scanning, image analysis, and time-of-click checks to catch threats that hide in attachments or QR codes. Attackers try to work around this by using compromised accounts, rotating domains, or warming up infrastructure to look trustworthy. Reputation is useful, but it is only one signal; strong filtering works best when it is paired with content inspection and identity controls.