Is SMEX DAG-aware?

No. SMEX does not even consider DAG as a cluster at all. Whenever you install servers, you will see a “NO” in the cluster column. For this reason, you need to manually add servers. You have to know that SMEX assumes that these servers function independently of each other.

Can it detect if a DAG is active or passive?

No. SMEX cannot distinguish whether a DAG is active or passive.

Can it scan a passive DAG?

No. DAG works on mailbox database replication. One will be mounted (active) and the other one will be unmounted (passive) while replicating. You can have both mounted and unmounted databases, which are part of different replications from different sources. SMEX always scans mounted databases but not unmounted ones. On the other hand, Transport Layer is scanned at all times. If the server is part of this, emails that pass will be scanned as well.

What will happen if one server goes down and the other one becomes active, which means that the database is mounted?

SMEX will start scanning the database.

For external SQL database during cluster installations, is it possible to use only one external database for all SMEX servers or do you have to use one database per SMEX?

It is possible to use one external SQL but not one database. For every SMEX installation, three databases will be created, which are the Configuration, Report and Logs. This is automatically done during installation. These databases do not grow much in Life of Product. The database size depends on how many reports customers create and keep, and how intense the logs are being treated. But normally, the product is quite small in size.