I've been trying to resolve an issue, but I'm having some trouble as I'm not very good with firewalls. My firewall seems to be changing information in the HELO command of SMTP traffic. It SHOULD look something like '220 mail.domain.com ESMTP postfix'. Internal to my network, this works fine. However, external the received response is '220 [192.168.0.1] ESMTP' which is my mail server's internal address (rather than it's external). This isn't an issue if I do a telnet to mail.domain.com 465 (alternate SMTP listening port), only if I try to telnet (or connect) to mail.domain.com 25. Does anyone know what could be causing this? I already removed my fixup protocol smtp 25 line from the config.
which firewall is this ?? can you please send us the static NATs/ACL configs ?? Are you able to see any translation happening on the firewall for 192.168.0.1 ?? If translation happens, the outside world should see the packets only as the public IP !! Are you using a local DNS for mail.domain.com to private IP ?? Is the same DNS talking to the internet DNS servers for name resolutions ??
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...