You might really not have the right access for it.. ASA works on layer 3/4 and allows a packet on port 25. but as it hits the server , your communication is on layer 7 and the application decides what you have to do ! So, this is more to do with Application. If you can telnet to port 25 and till you arent timed out, I do not see this as a network issue
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...