The search limit for the Archive Manager console Advanced Search can be found on the settings tab. By default this is configured for 10,000 items but can be increased as needed.
Note: Please monitor the memory on the archive server closely when increasing search results as larger searches will require significantly more memory to run. Memory usage on the archive server should never be allowed to reach 95% as IIS will not allow application pools to run if there is not enough free memory and this will prevent users from being able to open archived messages. We generally do not recommend increasing the search result limit past 200,000.