POP3 and PST search broken by March 2017 Update for Outlook 2016
An issue has surfaced with the March Update for the Current Channel of Outlook 2016 for people that are using an Office 365 installation. After updating to this release or higher, search stops working for POP3 accounts and PST files.
You can check whether your installation is affected by going to; File-> Office Account. When this states that you are using Version 1702 (Build 7870.2020) or later, then your build is affected.
When you are indeed using a POP3 account and/or pst-files and search is no longer working for you, the current workaround is to revert to build 16.0.7571.2109 which is the January 4 release, also being referred to as Version 1611. Microsoft is actively investigating this issue but no release date for a fix could be provided at this point.
More Info:
https://www.howto-outloo...by-update-march-2017.htm