From your comments, I understand that you would like to configure the PIX to allow hosts in DMZ to relay mail to inside Exchange Server.
Use static (inside, dmz) command which will let any user in the inside network access the dmz and another one to allow any device in the dmz to access devices on the inside. Also configure an access list on dmz interface to allow smtp.
You would also need to configure an access list to permit ip so that the devices on the dmz network can go out to the internet and also in to the inside network using any ip port.
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...
Table of Contents 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 an...