you can create fallback authentication mechanisms and i think in fact if like your AD went down users could still authenticate via the zimbra password. I think theres a section on this in the documentation. I"m not sure if it can be an 'either or' thing
as far as the must change password, figure out what attribute it is by doing
zmprov ga <account>
then you can do a script like
Code:
#!/bin/bash
for i in `zmprov gaa`
do
zmprov ma $i attributeName FALSE
done