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Cisco Cisco Email Security Appliance X1050 Informationshandbuch

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HAT Delayed Rejection FAQ
Document ID: 117960
Contributed by Viquar Ahmed, Cisco TAC Engineer.
Jul 16, 2014
Contents
Introduction
Prerequisites
What is HAT Delayed Rejection?
What are the benefits of HAT Delayed Rejection?
What are the differences in the mail log entries for a Delayed HAT rejected message and a message
with the Delayed HAT feature disabled?
How do you configure HAT Delayed Rejection on the ESA?
Introduction
This document covers some frequently asked questions about Host Access Table (HAT) Delayed Rejection.
Prerequisites
The information in this document is based on AsyncOS Version 6.1.5 or later for ESA devices.
What is HAT Delayed Rejection?
HAT Delayed Rejection allows AsyncOS to perform connection rejection at the message recipient level
instead of at the start of the Simple Mail Transfer Protocol (SMTP) conversation. This method of message
rejection allows SMTP dialog until the RCPT TO command, and thus provides more detailed information
about the rejected messages.
What are the benefits of HAT Delayed Rejection?
It has several benefits:
It enables AsyncOS to retain information for the blocked sender and recipient addresses of each
message.
• 
It prevents the sending Message Transfer Agent (MTA) from injecting the same message several
times once it has been rejected.
• 
It sends the bounce immediately to the sending MTA without any delays.
• 
What are the differences in the mail log entries for a
Delayed HAT rejected message and a message with the
Delayed HAT feature disabled?
These mail log entries show the message is rejected by HAT Delayed Rejection: