OS X's Mail application is impressive enough in its own right, but by adding Rocketbox you can make it much easier to search for messages. The app allows for the use of complex queries and advanced filters to home in on whatever you may be looking for - a real boon if you have a burgeoning inbox.
When a search is performed, the search term is highlighted in results to make t easy to determine if a particular result is the one you are looking for. If you find that you have too many result to look through, filters can be added to limit the search to individual people, accounts or status.
Rocketbox searches your inbox noticeably faster than Mail built in search facility and use of auto-suggest means that you may not even have to type your full query to find what you're looking for.
OS X's spotlight tool makes light work of scouring your hard drive for the files you need, and Rocketbox brings much the same feature to Mail.
A lightning fast way to search your inbox, however large it may be.