If you can already access that same server on port 80, it sounds like all your NAT rules are setup correctly. It sounds like you'll just need to add another access rule for TCP/389 for LDAP. Give this a try:
access-list OutsideIn extended permit tcp any host 12.x.x.1 eq 389
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...