To put all accounts for a domain into maintenance mode, blocking access you can do the following.
Put the domain into maintenance mode:
Put the domain into active mode:
# zmprov md mydomain.com zimbraDomainStatus maintenance
And to query the current attributes of the domain:
# zmprov md mydomain.com zimbraDomainStatus active
To query just the zimbraDomainStatus attribute of the domain:
# zmprov gd mydomain.com
Note: Only Zimbra admins will be able to login to a domain when in maintenance mode. Normal users will not be able to login.
# zmprov gd mydomain.com | grep -i zimbraDomainStatus