SenderBase Reputation Score (SBRS) is a numeric value that is assigned to an IP address based on information from the SenderBase Reputation Score. The SBRS combines the information from different sources to determine if the sender is legitimate or if traffic from the sender has been known to be SPAM. To do this, the SBRS pulls it's information from over 25 public blacklists and open proxies and then combines the data with global data from the SenderBase to assign a score from -10.0 to +10.0:
-10.0: Most likely a malicious sender/SPAM email.
0: Neutral, or there is not enough information received to give a score.
+10.0: Most likely a legitimate email.
The lower (or more negative) number, the more likely it is SPAM, where as a -10.0 means that it is guaranteed to be SPAM. While a score of 10.0 means that the message is guaranteed to be legitimate.
We provide you with these details to help you make decisions on if you believe the traffic is legitimately sent from your ecosystem/organization, or if it is a Phishing email sent by someone using your domain maliciously.
For further information on SBRS, please visit Cisco's website: https://talosintelligence.