Some standard parts of email delivery are going to work against you here.
While a shun or a TCP reset might be issued fast enough to interrupt a specific message, most mail servers are set to retry delivery in case of failures. The message may time out after a few days, but you have no control over that.
Also, shunning popular mail servers like hotmail.com might cause disruptions you don't want.
This really seems like a problem better solved elsewhere in the system.
Best way to block spam is on the email server unless cisco comes out with IDS signature that can control it. What i use is a software solution on our company exchange server to filter out domains from RBl list. Email me i will let u know in detail.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
[toc:faq]Introduction:This document describes details on how NAT-T
works.Background:ESP encrypts all critical information, encapsulating
the entire inner TCP/UDP datagram within an ESP header. ESP is an IP
protocol in the same sense that TCP and UDP are I...