Your internal PC tried to make a connection (DNS) to the outside but the translation failed. Could be due to internal error or config error. If that PC isn't supposed to make a DNS request, find out why it's doing it and stop it. If it is supposed to be allowed, post the message severity number (eg %PIX-6-305006), and make sure there is a NAT or static for it.
Your exchange server only has a static NAT for port 25 (SMTP). So when your exchange server is trying to go out on port 53 (DNS), it fails due to no static mapping - ie the pix can't perform the translation as there is no rule. So, you have 2 choices:
1) static (inside,outside) 184.108.40.206 xx.xx.xxx.xxx smtp netmask (ie remove the tcp and smtp so it can go out on all ports)
2) Stop the exchange server from making DNS requests.
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...