Here my GAL configuration works on 7.x.
Code:
# Externatl GAL configuration
# login as zimbra user: su - zimbra
zmmailbox -z -m galsync@domain1.com createFolder --view contact /_ExternalCompanyGAL
zmgsautil createAccount -a galsync@domain1.com -n ExternalCompanyGAL --domain domain1.com -t ldap -p 1d -f _ExternalCompanyGAL
zmprov mds galsync@domain1.com ExternalCompanyGAL zimbraGalSyncLdapBindDn CN=ad_user,OU=Users,DC=domain1,DC=com
zmprov mds galsync@domain1.com ExternalCompanyGAL zimbraGalSyncLdapBindPassword aqQgLw2q
zmprov mds galsync@domain1.com ExternalCompanyGAL zimbraGalSyncLdapFilter '(&(|(displayName=*%s*)(cn=*%s*)(sn=*%s*)(givenName=*%s*)(mail=*%s*))(!(msExchHideFromAddressLists=TRUE))(|(&(objectCategory=person)(objectClass=user)(!(homeMDB=*))(!(msExchHomeServerName=*)))(&(objectCategory=person)(objectClass=user)(|(homeMDB=*)(msExchHomeServerName=*)))(&(objectCategory=person)(objectClass=contact))(objectCategory=group)(objectCategory=publicFolder)(objectCategory=msExchDynamicDistributionList)))'
zmprov mds galsync@domain1.com ExternalCompanyGAL zimbraGalSyncLdapSearchBase dc=domain1,dc=com
zmprov mds galsync@domain1.com ExternalCompanyGAL zimbraGalSyncLdapURL ldap://10.5.5.3:3268
zmprov md domain1.com zimbraGalMode both
zmprov md domain1.com zimbraGalLdapFilter ad