I have the following configuration for an LDAP address book:
{
type = ldap;
id = global_contacts;
displayName = "Gemeinsames Adressbuch";
IDFieldName = cn;
CNFieldName = cn;
UIDFieldName = uid;
baseDN = "ou=contacts,dc=example,dc=com";
bindDN = "cn=sogo,ou=dsa,dc=example,dc=com";
bindPassword = ***;
scope = SUB;
hostname = ldap://localhost:389;
isAddressBook = YES;
canAuthenticate = NO;
objectClasses = (mozillaOrgPerson);
modifiers = (user1, user2);
listRequiresDot = NO;
filter = "objectClass=mozillaOrgPerson";
mapping = {
displayName = ("cn");
};
}

The used LDAP schema derives from inetOrgPerson, therefore "cn" and "sn" fields are required, but when creating a contact from SOGo (with all fields set!), the "sn" field is not set and the Contact creation fails.