The search result limit is part of the profile settings for each user. By default this is configured for 10,000 items but can be increased as needed.
To increase the search result limit in ArchiveWeb, start by clicking the username in the top right corner of ArchiveWeb and choose Manage Settings
Next click the Profile tab
On the profile tab find field for Maximum number of search results and increase the limit 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.