“.muttrc ldap address”
“mutt ldap”
“ldap script for mutt”
“ms exchange directory”
You will need to download one of the LDAP querying scripts for mutt. One of them is here. After downloading, edit the script to match your LDAP server and put lines like set query_command="/home/username/bin/mutt-ldap.pl '%s'" into your muttrc file. If you will add also bind editor "\t" complete-query , then you will be able to complete addresses using Tab button.
Note, that you can use the same script with MS Exchange, since it’s nothing more then an LDAP address book. :)