[exim] Problem with lookup ldapm and Active Directory

Hello,

I have a problem with LDAP lookup and MS Active Directory.
If I query "OU=MYOU,DC=MYDC,DC=MYTLD" the query is very fast and recipients can be verified.
The problem is that there are no public folders in this OU, so I tried asking "DC=MYDC,DC=MYTLD" but I have big delays of more than 5 seconds.

This is my script
1     ${lookup ldapm
2     {user="ADUSER"
3     pass="ADPASS"
4     ldap://ADSERVER/ADDN
5     ?mail?sub?
6     (|
7     (&
8     (|
9     (objectClass=user)
10     (objectClass=publicFolder)
11     (objectClass=group)
12     )
13     (proxyAddresses=SMTP:${quote_ldap:${local_part}}@${quote_ldap:${domain}})
14     )
15     (mail=${quote_ldap:${local_part}}@${quote_ldap:${domain}})
16     (otherMailbox=smtp:${quote_ldap:${local_part}}@${quote_ldap:${domain}})
17     (proxyAddresses=SMTP:${quote_ldap:${local_part}}@${quote_ldap:${domain}})
18     (uid=${quote_ldap:${local_part}})
19     (cn=${quote_ldap:${local_part}}@${quote_ldap:${domain}})
20     )}
21     {${local_part}@${domain}}{:fail: User unknown}
22     }

Do you have any ideas why this lookup takes so much time? I had to disable the check now.

Best regards,
Fabian