There is currently no standardized way nor a setting for doing as you described. Currently the only way is by a manual change. However, we’re receiving questions about this more frequently and consider improving this in a future release. I can’t say when.
If anyone is willing to do some manual changes here is a big picture on how this works in Zammad:
The scheduler starts the registered job every hour. This job checks all active backends. These are the LDAP and Exchange backends by default. The job then checks if the backend is valid, queueable, active etc. by e.g. requesting the interface of the backend which inherits the most of this from a base class.
Feel free to ask any questions.