When you search for email messages that contain a specific keyword in Microsoft Outlook in a Microsoft Exchange Server 2013 environment, Outlook returns 250 items even though you know that there are more results available. This occurs even after you click the More option at the end of the results list to load additional search items.
To fix this issue, install Cumulative Update 11 or a later cumulative update for Exchange Server 2013.
After you have installed the update, the default value is still 250, but you can edit the Microsoft.Exchange.Store.Worker.exe.CONFIG file to increase the limit of search results. To do that, you must add the following entries under the <appSettings> section as follows:
<add key="MaxHitsForFullTextIndexSearches" value="5000" />
Note If <appSettings> doesn't exist, you will need to add it after the </runtime> tag.
The above example will increase the search items returned to 5000. The MaxHitsForFullTextIndexSearches value can be between 1 and 1000000. Care should be taken with this value as setting this too big could cause performance impact on the server.
Once the above file has been edited, restart the information store service on the server for the change to take effect.
After you implement the resolution, unexpected behavior may happen to the results the Search-MailboxAuditLog command returns. When you run the command, the number of audit logs returned are unexpectedly capped at the MaxHitsForFullTextIndexSearches value no matter what you set for the ResultSize parameter.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.