Hi,
I have been wondering and I found a workaround for the problem. If you use samba passwords to access shares on some machine and ldap passwords for everything else then you can turn "Password does not expire" on in Samba Account Tab. The user will have to change his ldap password eventually if you set password expiration in zimbra. If users do not use windows domains then this is one of your options (if they use windows domain accounts then you can uncheck "Password does not expire" and they will change samba password instead of ldap
)