I use Emacs Unified Directory Client (EUDC) for completing email addresses from LDAP and BBDB databases. It’s nice to be able to complete names from LDAP when composing emails, obviously, but it’s also nice in Org mode to M-x eudc-expand-inline someone’s name into my notes.
When I first configured the EUDC LDAP backend for my environment — RHEL 6 ldapsearch, LDAP-over-SSL server — setup was very involved. There were lots of poor defaults, strange extra configuration files, function call requirements, and ldapsearch incompatibilities. EmacsWiki instructions were very long just to get sane “Givenname Surname <email@address>” completion in GNUS.
I filed a bug report with configuration simplifications, bug fixes and EUDC Info manual updates, and somehow I ended up as the EUDC maintainer. I’ve committed the improvements to the Emacs master branch; they’ll be released in Emacs 25.
If you’ve tried EUDC in the past and been turned off by its arcane configuration, you might want to re-read the “LDAP Configuration” section of the Info manual, and try again. If you still can’t get it working, file a bug report at bug-gnu-emacs and I’ll try to respond to it within a few days. Mention EUDC or LDAP in the subject of the report. Likewise, if you do get it working with hacks then let me know via a bug report.