See https://lists.samba.org/archive/samba-technical/2013-November/095826.html
There's a memory leak in ldif_canonicalise_objectCategory(), which triggered by LDAP searches like '(objectCategory=Persion)'. Zarafa uses filters like (objectCategory=Persion) or (objectCategory=Group) by default. This could explain the bug.
*** This bug has been marked as a duplicate of bug 10469 ***