We are currently using Exchange version 14.3 (Build 123.4).
It seems that every day when I come in users are complaining that search is not working in Outlook (confirmed on my machine). Users are using a variety of Outlook versions, but most are on 2010 or 2013. None of them are using it in cached mode.
I'm not sure what is actually getting it going again, but I've been trying the following:
Restarting the following services: "Microsoft Search (Exchange)", and "Microsoft Exchange Active Directory Topology" (plus all the services that require them). Between the two it seems to cover a fair amount of the exchange services.
The first day searches started working sometime shortly after I did that. All the others, I ended up doing ".\ResetSearchIndex.ps1 -force -all" from the shell. Granted it can take some time after resetting the index for it to build up again and work - if that is even fixing it at all. Perhaps just the time it is taking me to do those tasks is fixing the problem.
Any idea what might be going on?