Is there any solution to this? I want the result to include the value of gosaMailForwardingAddress from the Group LDIF, but not the Member LDIF.
It would look like:
# postmap -q testgroup@example.com ldap:/etc/postfix/mailing_lists_local.ldap
test.user@example.com,group_external@gmail.com

Group LDIF:
dn: cn=testgroup,ou=Groups,dc=example,dc=com
objectClass: fdGroupMail
objectClass: gosaGroupOfNames
objectClass: groupOfNames
cn: testgroup
gosaGroupObjects: [U]
mail: testgroup@example.com
member: uid=test.user,ou=People,dc=example,dc=com
fdGroupMailLocalOnly: FALSE
gosaMailAlternateAddress: testgroup@example2.com
gosaMailForwardingAddress: group_external@gmail.com
gosaMailServer: MailServer

Member LDIF:
dn: uid=test.user,ou=People,dc=example,dc=com
objectClass: gosaMailAccount
objectClass: inetOrgPerson
objectClass: organizationalPerson
objectClass: person
objectClass: posixAccount
objectClass: shadowAccount
cn: Test User
gidNumber: 1500
homeDirectory: /nfshome/test.user
mail: test.user@example.com
sn: User
uid: test.user
uidNumber: 1101
gecos: Test User
givenName: Test
gosaMailDeliveryMode: [L]
gosaMailForwardingAddress: user_external@gmail.com
loginShell: /bin/bash
o: Example Company
ou: Information Technology
shadowLastChange: 17486
userPassword:: <HASH>

mailing_lists_local.ldap Config 1:
version = 3
server_host = 10.10.10.1 10.10.10.2
search_base = dc=example,dc=com
query_filter = (&(|(gosaMailAlternateAddress=%s)(mail=%s))(objectClass=fdGroupMail))
exclude_internal = yes
result_attribute = mail,gosaMailForwardingAddress
special_result_attribute = member
leaf_result_attribute = mail

Result:
# postmap -q testgroup@example.com ldap:/etc/postfix/mailing_lists_local.ldap
test.user@example.com,user_external@gmail.com,group_external@gmail.com

mailing_lists_local.ldap Config 2:
version = 3
server_host = 10.10.10.1 10.10.10.2
search_base = dc=example,dc=com
query_filter = (&(|(gosaMailAlternateAddress=%s)(mail=%s))(objectClass=fdGroupMail))
exclude_internal = yes
result_attribute = mail
special_result_attribute = member
leaf_result_attribute = mail

Result:
# postmap -q testgroup@example.com ldap:/etc/postfix/mailing_lists_local.ldap
test.user@example.com

Again, what I want to see as a result is:
# postmap -q testgroup@example.com ldap:/etc/postfix/mailing_lists_local.ldap
test.user@example.com,group_external@gmail.com

I need something that does the opposite of leaf_result_attribute, and excludes the attribute (gosaMailForwardingAddress) from the expanded result, not the original one.

Another option would be to only return the value of gosaMailForwardingAddress if gosaMailDeliveryMode does not have "L" in it which indicates that mail forwarding is disabled for this account.