> Can anyone tell me, how this structure should look like? > Which entries are needed so Thunderbird will show the record?
The LDAP support in Thunderbird is currently a bit odd: http://www.mozilla.org/projects/thunderbird/specs/ldap.html
It should be fixed in the future (current on left / proposed on right): https://bugzilla.mozilla.org/attachment.cgi?id=166745&action=diff