The search function in any mail system is crucial especially if you use it for business. Microsoft Outlook search function is prone to some error and stops working for no apparent reason. It does not matter what mail you have, you can connect to gmail, hotmail or your own domain, the search function just stops working.
I have searched through all forums but no one recommendation worked for me. I even tried re-installing, running repairs etc.
Solving Outlook 365 search function not working
I think it has all to do with the size of the outlook.pst file which is the main data file for your emails. Once it reaches a certain size the Outlook 365 search function stops working.
If you don't create new separate data files your main outlook.pst will grow and get bloated. It can easy reach more than 1GB in size. If you use it for business and have mails as far back as 5 years, the total size can be 30-40GB. There is no way Outlook 365 can run smoothly with such a big file.
One solution is to archive regularly to contain file size, but I don't like it that much. I prefer creating data files to categorize all my mails. Also try and keep your main Inbox folder as small as possible. So unused mails are moved to other folders, keeping the main outlook.pst file in check. On my system I create the following additional data files:
So every week or so I move files from my main Inbox to these locations.
In any case, the moment when I reduced the file size of the main Outlook 365 pst file, the search function started working again.