Search Indexer add-in disabled (mssphtb.dll)

I'm having some issues with the search function in Outlook and I think it is because the Windows Search Email Indexer is disabled.

I tried to enable it but Outlook disables it every time.

Why can't I enable this add-in and how do I get Search to function again?

Search Outlook buttonThe Windows Search Email Indexer add-in (mssphtb.dll) is disabled in Outlook 2010 and later as Outlook 2010 and later have native support for indexing now and thus no longer needs this add-in.

To prevent any issues, Outlook 2010 and later are programmed to disable this add-in.

Part of Windows not of Outlook

The mssphtb.dll file is a part of Windows Search on Windows Vista, Windows 7, Windows 8 and some early Windows 10 versions which exposes itself as an add-in in Outlook. It is also known as the “Outlook MSSearch Connector”.  In addition, it also exists on Windows XP systems on which Windows Search is installed. By default you’ll find it in;
C:\Windows\System32\mssphtb.dll

While Windows Search no longer needs it to index the contents of Outlook 2010 and later, it is still required to have this add-in enabled when you are using a previous version of Outlook and want to have your e-mails indexed.

Solving Outlook Search issues

So, whatever your search issues in Outlook 2010 or later may be, it is not caused by the fact that the Windows Search Email Indexer add-in is disabled. For solutions to solve Outlook search issues see; Fixing Instant Search

Windows Search Email Indexer is listed under the Disabled Application Add-ins section 
Outlook 2010 doesn’t need the Search Indexer add-in.