Do you enable the search in OWA?

If search is not enabled you will get this message in OWA:

"Search results may take a long time to appear because Microsoft Exchange Search is unavailable. Results will not include matches in the email body."

This is how you fix it:

To diagnose Exchange Search issues

Is the MSExchangeSearch service started on the Mailbox server? If Yes, go to Step 2. If No, use the Services MMC snap-in to verify that the MSExchangeSearch service is running:
- Click Start, and then click Control Panel
- In Control Panel, double-click Administrative Tools
- In Administrative Tools, double-click Services
- Verify that the Microsoft Exchange Search Indexer service is started
Is the IndexEnabled parameter configure to true for the mailbox database of the user? Run the following command in the Exchange Management Shell to verify that the IndexEnabled flag is configure to true: Get-MailboxDatabase |ft Name,IndexEnabled
Run the Test-ExchangeSearch command for the user: Test-ExchangeSearch -Identity username[at]ssw.com.au
Check Event Viewer for search-related error messages. Check the Source: MSExchangeSearch Indexer and msftesql-Exchange events. For more information, follow the link on the event log

To Rebuild the Full-Text Index Catalog Using the ResetSearchIndex.ps1 Script

Start the Exchange Management Shell.
ResetSearchIndex.ps1 -force -all
Wait a couple of minutes to the index be created
Run the command to verify if the index was created
GetSearchIndexForDatabase -All