[Reference: https://www.cisco.com/c/en/us/support/docs/security/email-security-appliance/118136-qanda-esa-00.html, , Connection Behavior setting allows you to specify how the Cisco Email Security Appliance (ESA) handles incoming connections from different sender groups. You can choose from four different settings:, Accept: The ESA accepts all connections from the sender group and applies the mail flow policy settings to the messages., Throttle: The ESA limits the number of concurrent connections and messages per connection from the sender group. This can help reduce the impact of spam or malicious traffic on the ESA’s performance., Reject: The ESA rejects all connections from the sender group and returns a 5xx SMTP error code to the sender. This can help block unwanted or abusive senders from reaching your network., Test: The ESA accepts connections from the sender group but does not deliver the messages to the recipients. Instead, it logs the messages and marks them as test messages. This can help you test the mail flow policy settings before applying them to real traffic., To modify the Connection Behavior setting for a sender group, you need to do the following steps:, On the ESA, choose Mail Policies > HAT Overview., Click Edit Settings for the sender group that you want to modify., In the Mail Flow Policy Settings section, choose one of the options from the Connection Behavior drop-down list., Click Submit and commit changes., ]