Thanks for the update.
I'd like to ask it again since you didn't mention it in your reply:
Are you using online Exchange mode or cached Exchange mode? Do you have the
Download Shared Folders turned on under Account Settings?
I ask this because it searches based on different indexing depending on the different settings I mentioned in the question. It will help us to understand the issue more clearly if we know the answer to the question.
In addition, we may also try using Advanced Find to see if it works. To do this, open Outlook 2013, click Ctrl + Shift + F to open the Advanced Find dialog. Click the Browse
button and select the shared mailbox, and then check the check box before
Search subfolders.
Please let me know the result.
Thanks,
Steve Fan
Forum Support