That is only for Exchange mail relays through the PIX. Everything on your network should gateway at the PIXs inside interface. The static will be setup between the mailservers real address and its MX record. The PIX proxy arps for that address and it must be unique and unused on the outside segment. If you are not doing NAT, use the same address twice in your static. Then, setup your conduits allowing SMTP and/or POP3. If you want to use NetBios exchange mail, you have to open a lot of conduits and its pretty insecure so Id just stick with SMTP as your Internet gateway. This link should help:
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...