If you cannot telnet to the mail server address from the outside on port 25 check and see if your outside ACE's are getting any hits, if not you may need to reset any routing device in front of the ASA if you have control over it. That way it can build a proper arp table. That was my issue when I upgraded from a pix to asa. Check the "Outside access in through asa 5510" post. Exact problem with smtp traffic.
Configuration is OK, you maybe re-check the IPs and then run the packet-tracer command (available on ASA 7.2 and later only). Or a simple telnet as others suggested. Also make sure the SMTP server has a default route and the service is working properly
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...