We have a simple exchange 2013 setup with one CAS server, one mailbox server and one archive server.
This morning we had a brief issue where outlook clients were showing as disconnected.
Restarting outlook on my machine solved the problem and it was showing as connected.
On mailbox server CPU and memory usage was high but no errors.
test-servicehealth and test-mailflow were ok.
What else can I check to find out what happened.